The postings were on topic and definitely not spam, but they were treated as such. Naturally, this could also cause good email spam filters to also block your emails. Before you create your email signature, it's a good idea to sit down for a minute and determine what your objective is. If you want to advertise your web site, it's a good idea to include a small ad and a hyperlink. If you are a salesperson, it may be wise to include your phone number and extension.
Some people like to include a favorite quote.
Not only is it considered tacky, but these things can trigger spam filters and get your emails automatically deleted. It's better to include these items on your website and put a link to that site in your email signature. Do not include profanity or harsh language. 900 numbers can also trigger spam filters. Be sure to use standard formatting in the signature.