I own a BMW M3. ('04) I want people to see my car and KNOW that its a "M" not just a regular 3 series. Any ideas on that?

if the person looking at your car is a real bmw lover, he or she should already be able to tell by looking.

They have extra emblems that you could buy to put in places that they dont come stock. You could also get some side skirt decals with the M badge. Basically a real BMW lover would know it is a M3 and should. check out these sites they have loads of M3 extras
hope this helps

don't put an "M" badge on it, make you car a sleeper! you can have lots of fun this way, blowing away those boy racers. Another thing, someone may steal your car for chop shop and send it to China or just for joy ride if they know it's M3.

Well they should be able to tell by looking at the grill on it..

An M3 is blatantly obvious to anyone that knows anything about BMWs, but by your question, I'm guessing that you may not have the M3 badge on the back end is that right?
The E46 M3 is most easily discernible by it's side gills in the front quarter panels, the mirrors, the hood, the flared fenders and the Quad Pipes in the back.
Even if you don't have the M3 badge on the back these attributes are telltale of an M3 anyway so who cares? In fact it might make it fun when a Japanese rubberband rocket pulls up next to you "THINKING" they can blow your doors and you can leave them behind calling their moms asking "why mom"??? hahaha