Hello again!

This time these signs are properly tagged.

The traffic signs added in this commit are using the "Traffic signs_ES" JOSM tag preset by yopaseopor.
This adding of traffic signs comes from an agreement from the Catalan community for mapping the traffic signs using his preset and with the country IDs in traffic_sign:id=, human-readable values in traffic_sign=, and adding a relation similar of the type=node for tagging the traffic signs, where is attached and the place of the road where it starts to take effect. The plugin in question has been updated several times to reflect and be able to work with all of this. Think as if it were a "regional standard", it was talked on the Telegram community group, and no one opposed it.

This traffic sign tagging scheme is very complex and detailed, but this also causes it to be super verbose and state the obvious in many cases. 
But also I consider that having a verbose scheme is good because it allows more flexibility. For example, if there is more than one destination in a single direction, there are numbered tags for specifying all the destinations.

The fact of splitting values into different tags, makes them easier to edit and also, if in the future, the system for tagging traffic signs changes (again), then we would be able to easy adapt the current signs into the new system via automated edits; instead of having to potentially redo the signs because all the values were mixed.

This explains the new tags, although this commit has added 3 different roundabout destination signs (one of them being the one you've linked), so I'm pretty sure that most of these tags are also in the other signs.

The only other (simpler) standard for roundabout destination sign tagging that I know is the Spanish roundabout sign preset from the RoadSigns JOSM plugin (https://wiki.openstreetmap.org/wiki/JOSM/Plugins/RoadSigns).
Using this plugin, the sign of the node you've linked would look like this:

destination:colour=blue|white|blue
destination:ref=A-27|C-37|A-27
destination:sign=pier;plane;ave||
destination=Tarragona|Alcover;Reus;Prades|Valls;Lleida
junction=roundabout
traffic_sign=ES:s200
turn:destination=left|through|right|slight-right

For this sign, this preset works flawlessly. The tags are short and few, and everything fits perfectly. I really like how it looks, it's simple yet effective.
Unfortunately, this is also a pretty simple roundabout sign, and more complex signs would have great difficulties for "fitting in".

On the same roundabout, on the exit leaving the A-27 and entering the roundabout from the south, there's also this sign:

- OSM node (mapped with the same preset as the one sign you've linked): https://www.openstreetmap.org/node/12645203477#map=19/41.270094/1.232110&layers=N
- Bing Streetside: https://www.bing.com/maps/?cp=41.269972~1.23202&lvl=15.0&pi=3.4&style=x&dir=350.4

You can see that the left roundabout exit has C-37 as the main road reference and Alcover as it's primary destination, but there's also a secondary reference of C-14 with Montblanc.
This is because Montblanc is an important city, and to reach it, you have to first go to Alcover via the C-37, and once there you have to grab the C-14 road towards Montblanc. This roundabout does not directly connect with the C-14 road.

How would these references be tagged in the RoadSigns plugin? My guess would be "destination:ref=C-37;C-14|A-27|C-37", but such an approach will clash front-facing with other signs that have several primary references.

Signs like this one: https://www.bing.com/maps/?cp=41.141731%7E1.233511&lvl=17.0&mo=om.1&pi=0.4&style=x&dir=213.3
(not mapped in OSM yet, I think)

This left roundabout exit goes towards Tarragona and has the road references of A-27, A-7 and T-11. This is because after the left roundabout exit, there's a brutally massive junction in which you can go to either A-27 (the main one that this roundabout connects to), the A-7 or the T-11, and you can enter Tarragona through any of these three.

Following the RoadSigns plugin, it's destination:ref would look something like this: "destination:ref=A-27;A-7;T-11||A-27", and this tagging makes sense here, but now we still have the question of what to do the C-14 Montblanc case of the previously-mentioned sign.
Placing "C-14 Montblanc" with both secondary reference and secondary destination text all as a secondary destination (or as a new line of all the destinations together) might work, but this method will probably not highlight the C-14 reference text as much as the other references (thus defeating the reason of why we place references in other tags).

Do you want another example of a complicated roundabout sign? Here's a big one: https://www.bing.com/maps/?cp=41.279575%7E1.257056&lvl=17.0&mo=om.1&pi=-3.2&style=x&dir=251.5
(this one is not yet mapped in OSM, I'll probably tackle it once I go arround the Valls beltway)

On this sign, the RoadSigns plugin would have problems rendering the white background of the left exit while being yellow for the secondary destination of Camp de Tarragona with the AVE symbol.
And then there's the hodgepodge of the right exit, with a primary reference of the N-240 road towards Valls and Lleida with white background, a secondary reference of C-51 towards El Vendrell with a white background, and a tertiary blue background box of the top-level motorway AP-2, with European route reference E-90 and the sign of paid toll.

Representing this sign using the RoadSigns plugin would be impossible, or we would have to do a lot of compromises and "tag approximations" that then we would have to "decrypt and unroll" should we want to render this sign into an image or a model or interpret it for whatever reason or propose may arise.

The approach of the RoadSigns plugin works well in simple signs, but unfortunately fails on the more complex ones. The current, by being verbose as heck, we have a chance to adapt it better to whatever surrealist painting of a sign comes. I don't know of any other traffic destination sign tagging system other than the one used here and the RoadSigns plugin, but if there is, it'll probably need more tags than normal for specifying these and all the edge cases that may arise, and then the current situation of new tags will also reappear.

Sure, this complex tagging scheme is an overkill for simple signs like the one you've linked, but will be useful for better detailing the more complex signs. And there are many other tagging schemes in OSM that are overkill for very small features (for example: a very short bus/metro line that still needs plenty of tags for the ways, stations and relation about names, operators, networks, and such…).

Traffic signs are very complex, there are many of them, and very different, so it makes sense that it's tagging system is also complex and detailed.


And for your point of the Tarragona pier, plane and AVE symbols being all in different destination symbol tags, sort-of implying that there are all alone in new lines; I agree with you.

Due to splitting values into their own tags, this also means placing values like those symbols in independent tags. Although, I suppose that there will be very little confusion; as it is highly unlikely that these symbols will be alone in their lines. I will probably change this in an upcoming commit, because I also don't like it much xD

Sorry for such a massive reply. I hope that the examples that I provided help in understanding the logic of this scheme.