Heh, I was asking the same question. I use my friend code when I promote the game outside CoE servers but on forum ... I don't know.

Up until a few months ago, you could still enter friend codes afterwards if you forgot to do so at registration. I reckon people simply forgot or neglected to remove them.

As for random codes, you could get lucky -_-

You don't need to register to the forum to visit and browse through it. Registering is only necessary if you want to post or purchase a package. In which case, who knows, you may be lucky enough to impress a random visitor enough with your comments that they'd put your friend code in when they do register. Though more like it's just good to have there so your mates that you referred to here from outside can easily access it when they do.