Stigmatizing one's employment history only impacts people who are trying to switch from advertising to a different industry. This means it has the effect of locking employees into staying in advertising.
I understand that the logic goes that people will avoid going into advertising in the first place if it limits their employment choices, but that assumes there isn't enough work to stay in advertising. If advertising is already a profitable career path, switching industries later is not a significant consideration now, and your proposal actually makes it easier for advertisers to hold onto talent.
We should be encouraging people to get out of advertising, not stigmatizing it.