I normally click on them and open their equipment window then swiftly click another NPC and pretends I am interacting with them, whether it is a shop/leve NPC or those with normal conversation, anyone will do.

If they notice you noticing them, just smile and wave then run off with your mount.
Or if you're into RP or something, put up that "/em shrieks a 'kyaaa~' because <t> noticed him/her." macro.