I'd have to ask again on in the server if third-party signage is enough verification for a trail name. I don't see why it wouldn't count, in this case, if they are more permanent installations rather chalk writing on rocks or the like. 

If you were to use an image hosting site like https://imgbb.com/ you should be able to upload example images and link them here. You are also welcome to contribute to the discussion in the OSM US Slack server where you would be able to upload images directly rather than linking them through an image hosting site.