Perhaps you are referring to a set of characters that are unique to
you. The spammers put them there to identify you, like a Social
Security Number. Since each is unique, they know who accesses their
web site or responds to their e-mail. Even if you don't think you are
telling them your name, you are, because of this.
For example, if I arbitrarily assign "DCl397XE" to the address
"(e-mail address removed)", and I get an e-mail than contains "DCI397XE", I know
it is from "(e-mail address removed)" no matter what the address says.
Similarly, if you access abcd.spam_R_us.com/DCI397XE, I know it is in
response to e-mail sent to "(e-mail address removed)".
I was once told that I had not returned my anonomous questionaire at
work. They got very upset when I asked how they could know that since
it is anonomous. They got even more upset when they found out I looked
at another persons blank questionaire. I was looking for what made
each unique so that they knew I had not turned mine in.
When I asked why looking at another person's questionaire BEFORE it
was filled in, was wrong, they hit the ceiling. I never did find out
what the marking system was, but I know there was one. They sure were
pissed that I realized it, LOL.
