To extend what Mike said, check the transmitter for the frequency. If it's 75.something Mhz or says anything about 75Mhz or has a channel number above 60 then it's legal only for surface use, boats and cars.

If it's 72Mhz, or channels 11-60, then it's for aircraft only.

If it's on 27Mhz (which often have single digit channel numbers), then it's legal for both uses.

Also, note that 75mhz systems often do not transmit as powerful of a signal as 72mhz systems since the RX normally doesn't go as far away. With a park flyer, you won't get as far away as you might with a larger plane, but it's still something to watch for.