Is it safe to market on forums? My answer would be it depends how you go about it.

The first thing to do is to find some forums that have a direct link to any product you are promoting. Next read the forum rules. Some allow a URL to be placed in your signature box, but that is not always applicable.

Always read some of the forum comments before you start putting anything on it. Perhaps there are some questions on the forum that you can answer. This would be a good time to put a comment. Your comment is going to be able to be viewed by all members of the forum so make sure of your facts before you put anything.

There may be a discussion going on that you can add relevant information to.

Try to get yourself known on the forum. The more people see you taking part in discussions and comments, the more times your name is going to be seen. Just like in email marketing you are building up the trust factor. You will get to be known as a go-to person who helps others. As with any marketing, it always pays to be honest. The dishonest ones are very often found out.

Always, and I cannot repeat this often enough, always follow the forum rules! It is very easy to get reported and banned from a forum for not following the rules.

There is no reason why you cannot be a member of many forums, and it is sometimes useful to join a forum that has a tenuous link to your subject matter.