RM Skill: Undisclosed
What you want to do is edit your game's exfont.
Basically, RM2k/3 has these symbols you can insert in messages by typing a dollar sign followed by an upper or lowercase letter (e.g., $A). These icons are embedded into your RPG_RT.exe file (the file you use to run your game) and you'll have to use another program to edit it.
Some of this is in the rpg2003 help file. $A is a sword, $B a shield, $C is a magic star. Alot of the other stuff is zodiac symbols and such.
It took FOREVER to figure this out. Damn, I could swear I made a tutorial of it (pretty much everything else).
Okay, look there's a program called resource hack. Use it to open the RTP.exe
There should be a file called something like 0. Expand that, and look for picture files or something. There's about two major ones, the opening picture (that says Enterbrain, that you can tweak alot to brand name yourself, but since it's probably illegal, I'd also credit Eb! somewhere in the corner to be safe), and the other thing is something called Exfont. You export these as like black and white bitmap or something, edit it, and then import them back into Resource hacker.