I heard some people complained that pidgin does not show the messenger protocol for the buddies associated with your account. Actually this feature was indeed incorporated in Pidgin, only it is not enabled by default.
To enable the it, you only need to go to Buddies->Show, and select Protocol Icons option. Pidgin should display messenger protocol icon on your buddies list.
Here’s a screenshot which explains the step
From the screenshot you can easily spot which buddies are from jabber protocol and Yahoo Messenger protocol. I hope this particular tip would be useful to you!