Vehicle/Heli question

I've looked and watched videos, I haven't found an answer to this. I apologize if it's basic and already answered.

When you buy a vehicle at a vendor, I know you get a honk to designate which one is yours. But can some other random player go up to it and just get in it and fly/drive off before you get to it? Or is it locked to just your character until you get into it?

I know that you once you're in, you can unlock the doors to just your squad and whatnot. I'm mainly talking about when you first purchase the vehicle, and you have to run over to it. One of my biggest pet peeves is when someone steals your vehicle when you get out for a second, or in this case when you buy it and have yet to actually get into it for the first time.

Thanks, looking forward to playing this game so much!