Pedestrian-only crossings of public roads in the UK are *never* marked with dashes. This is defined by legislation, specifically TSRGD 2016.

If it's a signalised crossing (pelican or puffin), dots may be used, but are not a legal requirement. These are also crossing=traffic_signals, not crossing=marked

If it's a zebra crossing, dots may be used in addition to the zebra markings.

If there is a double dashed line transverse road marking between a crossing over a side road and a main road, this is a give way marking (mapped as a separate highway=give_way node). It has nothing to do with the crossing, which is likely to be crossing=unmarked crossing:markings=no

The wiki may help you here https://wiki.openstreetmap.org/wiki/Key:crossing:markings