Paintball guns look less like real firearms to people WITH hoppers and tanks on them. However, bad idea to run around with a "functional" paintball gun due to laws. Especially if you're running around in a public park like some kind of whack job who people assume is about to go postal.
It doesn't really matter if the marker is not "functional" due to no air tank/air pressure etc. People will freak out if you're running around with the iconic pistol grip/trigger frame in your hands. Just don't go there and save yourself a lot of headache, even if you are right or wrong.