I think these markings were not regarded as traffic signs (and are still not) – hence their absence from TSRGD. They were purely intended to be used by those operating the camera and not expected to convey “warnings, information, etc” (the definition of a traffic signs) to road users.
Making them ribbed, though, implies you are trying to attract road users’ attention with them. I don’t know where this idea comes from, and I would have thought it unlawful.
I think you can continue to place these markings in much the same way as you can use coloured road surfacing – it’s not considered a traffic sign. But I would question the lawfulness and usefulness of making them ribbed.