I haven’t found any specific regulations, although regulation 14 of the Workplace (Health, Safety and Welfare) Regulations 1992 does mention something.
The following is taken from the Approved Code Of Practice document of the above regulation (paragraph 150).
150 A transparent or translucent surface should be marked where necessary
to make it apparent. The risk of collision is greatest in large uninterrupted
surfaces where the floor is at a similar level on each side, so that people might
reasonably think they can walk straight through. If features such as mullions,
transoms, rails, door frames, large pull or push handles, or heavy tinting make
the surface apparent, marking is not essential. Where it is needed, marking
may take any form (for example coloured lines or patterns), provided it is
conspicuous and at a conspicuous height.
I would say as long as the window is clearly marked, there shouldn’t be a problem. If there are children and adults, then markings at 2 heights should be more than adequate.
Ivan