I hope I haven't missed the subject while searching. So:
How to flash those two small letters in tray programmatically?

You could maybe use /tray along with several image/ico files (or an icon library; .dll or .icl)
Lot of work for minimal gain though IMHO

https://forums.mirc.com/showflat.php?Cat=...amp;amp;fpart=1
That's why.
There are NO icons with lit I and/or R in mirc.exe, where to search for them?

I know why, I just think it's too much for too little.. thats my personal opinion. (IMHO - In My Humble Opinion)

However... they are not icons, look at the bitmaps

IMHO I know what's IMHO.
So the question is still open - I want to be sure is there a waiting channel message or not?
If they're bitmaps, how to use /tray with them?

Google is your friend.

Thanks, my friend in that case will be VS.NET. But I agree - too much effort for the little thing. So I think I'll better move on with that thread...