I'm not aware of any markings or certifications. And ending the list that way, I wanted to suggest a whole hinterland of considerations, rather than elevate table choice particularly.

But with those caveats, there are three issues with tables I've faced as a wheelchair user. In order of being increasingly common:

1. Wheelchairs are wide. I can't get into tables with legs a small distance apart. And the table is useless if I am too far away from it or I am side on.

2. A powered wheelchair is particularly tall, so short tables cannot be accessed. There were some I couldn't access in a manual chair also, particularly those with lips around the top. Or bolts and hardware on the underside that are painful to whack knees into.

3. Tables with a single central base don't allow wheels to enter on the floor under the table.

My disabilities are acquired. So I largely ignored the issue when I was running my businesses. As such I don't know about formal best practices or certifications. Honestly my best advice would be to rent a wheelchair for an afternoon and try it.

What country?

For maximum accessibility, a powered desk that raises or lowers is ideal to account for more situations.