I'd go. It's likely the people at the bank's table would be HR people or recruiters, and not people from your branch. But give the table a wide berth just to be certain,

Go. People working tables at a job fair are likely pretty much confined to staying in that immediate vicinity, likely are not people you'd work with regularly, and are probably too busy at their table to pay attention to those at other tables. GO, if you want, and don't worry about your employer.

I don't think it would be a good idea to go. Many companies fire anyone whom they learn is looking for another job.

If you are spotted then say you went with a friend.

Stop stressing, we are allowed to look at different opportunities.

You know, on more than one occasion, I have found myself at a dead end career wise where I went to my supervisor my career aspirations. My supervisors were understanding that the job I was in was not going to lead to advancement in my desired career goals, and was able to search for new employment without any hard feelings or sneaking around.

So, try the direct approach. Go tell your boss what career goals you want for yourself. When he/she tells you that isn't going to happen where you are at, tell him that you understand and hops that he understands that you'll be looking for a new job.

Well, how are you going to explain your absence from your job that day? You might as well let your managers know that you are looking for something else.

Go, but steer clear of the bank's booth until you can get a look at the people there.

???

Your situation is not unique. Contact the organizer of the job fair and see how they typically handle this situation.