Just give the toggle mask to anyone and everyone. How you react IC to someone in a mask in a situation where you think it's strange to wear one is down to each individual.
If company's want to make it a rule that their cabbies, mechanics, news reporters or whatever can't wear them on duty (although that would be common sense anyway), then they can set that rule.
Didn't read all this thread but as someone else said there shouldn't be some mystical power that stops you putting one on.
As for PD. I would also agree that only SWAT and Detectives should be allowed to put them on duty as an IC rule. If a detective decides to wear a mask it's up to other people to be suspicious of them if they want to be. Who wouldn't be suspicious and play things safe around someone in a mask that they didn't know. It's all about playing your criminal smart and playing your cards close to your chest.
People wearing masks has become too much the norm around the city. A mechanic refused to work on my car when I was on my alt and in a mask which I thought was good RP from him. If you are in a mask people should look at you with suspicion and question you about it if you try to interact with them wearing one, Cops would also be a lot more likely to question you in regards to it.