iPhone Syncing Issue

I use both a iMac and a MacBook Air, and originally used the iMac to sync my phone, only doing so once or twice on my MBA.

I'm now moving away and will only be taking my MBA, but when I do sync it on this machine it consistently deletes everything when syncing, so I have to put eveerything back on.

Is there a way to prevent this from happening/making it think it's syncing with my iMac?

Thanks in advance