Originally posted by Randy:
My understanding is that TM indicates that you are CLAIMING a trademark, while R indicates that the trademark is REGISTERED. Both are legally valid, but in the case of a registered trademark you have papers to back up your claim so it is more enforceable in court. While waiting for confirmation of registration from the patent office a company would use TM. This is just my understanding - I'm no lawyer mind you.
That's correct. If you go through the effort of registering a trademark (which usually involves a fairly expensive search to see if anyone already has your mark + paying ~$300 to actually register) it not only proves that you've done the work and own the mark free and clear (although it can be challenged), but it puts the burden on the guy suing you (or the guy your suing) to show that your mark infringes (or that theirs doesn't, as the case may be). Just doing a TM serves notice that you claim the mark, but haven't actually registered it. You can notice the difference pretty clearly on a fast food menu. McDonald's will be ®, but the slogan "You deserve a break today" will usually be TM. (Actually, if it's a popular slogan, they'll register it eventually).