I don't know of an identifier with the information, but I do know that with a dll call, mirc passes its hWnd Id through the function. if you're planning on modifying mirc, just use a dll call to say, save it and export it to a file, then reference it. it's a cheap way of doing it, but could be done. Additionally, you could take the harder approach and loop through the active applications being run. You should be able to identify mirc by its titlebar text..
I haven't gotten much into fooling with other windows other than my own, butI've seen it done before.