Marking is a quite rare phenomenon. DFing is much more common.
In my 35 years in, I knew the policy exists, but never heard of anyone being marked. An 50+ born in elder in my congo also never heard anyone being marked in a talk.
Until a sister in my congo yelled at and insulted an elder in the kh. On her way out, she did the same to an other elder. She also somewhat assaulted this elder by grabbing/pulling his tie while shouting at him. Her husband stood by and did nothing.
Since they refused to talk to elders after that, and wouldn't apologize, they were 'marked' in a talk. Without naming them, first the marking procedure was explained ('marked men are not DF, but don't socialize except at meetings. When talking to them, encourage to set things straight with Jehovah'). Then the unruly behavior (shouting at and assaulting other JWs) was explained as bad behavior. So far, it didn't help the elders much as they are still waiting for their apologies...