Q: I'm running  Mac OS X Lion 10.7.5 (11G63) on a MacBook Air, can't get the AppleTV icon to display so I can use Airplay mirroring.  Suggestions?

Hello there, dml5669.

The following Knowledge Base article provides great information for troubleshooting your issue:

iTunes: Troubleshooting AirPlay and AirPlay Mirroring

http://support.apple.com/kb/ts5209

Particularly:

If the AirPlay icon doesn’t appear in iTunes

Ensure that you followed these steps to use AirPlay in iTunes.

If the AirPlay icon still doesn't appear, try one of the following steps:

• If you want to AirPlay to an Apple TV, ensure that AirPlay is enabled on the Apple TV.  From the Apple TV main menu, go to Settings > AirPlay. This should be set to On.
• If you want to AirPlay to an Airport Express, ensure that AirPlay is enabled in the device settings.
• If you want to AirPlay to a 3rd party AirPlay-enabled device, refer to the user guide.

Thanks for reaching out to Apple Support Communities.

Cheers,

Pedro.