Many 240vac devices have no need for a neutral, so a 2-wire cable (plus ground) is more than sufficient to run it. You'd reidentify the white, neutral wire (tape or marker will work) if you want to do it correctly, but that's not always done.
A two-pole switch can be made to look the same as a single pole one, but most of those do not handle 30A (20A is fairly common as is the ability to switch 240vac circuits). If you pull the cover off of the switch, you may be able to tell, and it may have the specs on the front, but on the back is more common, so you'd need to pull it out of the box. Best to remove power first, though. A 2-pole switch would likely have 5-connections: L1-L2 in, L1-L2 out, and the safety ground. A simple two-pole switch would have three, L-in/out, and safety ground. Depending on how old the installation is, it may omit the ground wire.