Pure theoretical here, based on the thread about "Do you NEED to be certified to dive"
Let's say you are down at a local shore dive site getting geared up and you glance over at another diver about to splash whom you do not know. You notice they have all the normal gear one would expect and seem reasonably competent, but that their tank has a sticker on it that says "For paintball use only".
Would you feel compelled to say something or "hey, whatever, it's their dive"?
Now I am assuming your talking about a scuba purpose S80 with diving valve that you see lots of people use to fill paintball tanks.
Well im sure everyone is going to chime in on this and have very strong opinion, but personally I think I would just keep to myself as
@AJ mentioned a tank is a tank. If your really really worried you could just mention to them but I'm sure they would have a good reason.
Just because it has sticker like that does not mean it is dangerous. Lots of people use scuba tank and get them filled at scuba centers to use them for paintball.
Maybe the guy/gal actually uses it for paintball and then today they deiced to go diving with with
Mabey the guy/gal bought the tank used and it came with that sticker on it
Maybe they put that sticker on there to ID it as there paintball tank over there regular diving tanks but today they decided to use that one
Just because there is a sticker on it does not always mean that is what is in it. Im sure we have all put Nitrox in a tank marked Trimix or a deco gas in a tank marked O2, or air in an argon bottle, etc. etc. etc.
All the time I mark my inflation cylinders (filled with air) with a sticker that says "Wing/Suit Only" but when I only have hypoxic trimix and O2 on my unit ill use my inflation cylinder for air brakes.
But that being said is it good practice to have correct labels and if you do not then you need to make it very clear with your team mates about the change. However the actual exact gas content and verifying that it truly is that is a MUST!! Never go diving with tanks that do not have the actual mix marked on them and you personally analyzed them. And personally if it was my tank I would have just put a strip of white tape over it to cover the "paintball" label for less confusion