If you were topping up, they wouldn’t see the cash amount paid in until it had topped up after handing over the cash. So they would need to leave their position in the queue and follow you in the hope of spotting how much you paid in. The money being paid in might not be sourced from your salary too.
Edit: sorry I read that quick, I assume by hiding salary you mean your current account balance? That would make more sense.
I think it’s been mentioned before, I’ll see if I can find the thread. It was very recently mentioned by another person.
The thing is if someone saw you had say £100,000 balance or £10,000 balance or £1,000 balance what does that change? I wasn’t going to rob him but 
if I nick his phone, chop off his thumb, interrogate for pin, I could transfer some cash out to my own account and then get swiftly nicked… 
If they are nosey type then it’s probably either ‘oh they are doing alright for themselves’, or a smug ‘I’m doing better than them’ in their head. Who cares. 