Before you start spamming forums you must know and understand spamming goals. Understanding your goals is a very important part of spamming. Please keep in mind that your goals are separate from your plan. Here is a good goal list I've compiled, and I advise you to keep these in mind.
* You should be noticed. Spamming without anyone caring or even reading the spam is such a waste.
* You should tick people off. If everyone thinks you're great then what's the point? (note 1)
* You should enjoy yourself. Your ultimate goal should be to have a good time. Feel free to laugh out loud while you're spamming.
* You should gain some experience. Every time you spam make sure you learn something, you want to perfect your skills.
* You should aim to annoy/irritate. You should try and annoy/irritate as many people as possible with the least material possible. This can include pictures as well.
Here are some ideas to get your brain going, some of these are from the techniques.
1. Post every post in a very hard to read text color. Like this
2. Speak in binary or another language.
3. Make all of your text a link. Pretend its an accident. Oops.
4. If the forum allows HTML in the posts, put frames in all your posts. More then one scrollbar can be very fun.
5. Put a huge transparent signature in your signature
6. Use way too many smilies. I mean way too many.

7. Double post every time you post. Pretend its a browser bug.
8. Request as many graphics as you're allowed. Post tons of code support questions, and make them really hard.
9. Submit useless stuff to indexes. (IE. A table to the html index, a blank forum to the forum skins, etc.)
10. Make all of your posts rhyme.
11. Use a thesaurus so your posts don't make much sense.
12. Start a chain pm.
13. Search for very old threads and reply to them. Bring back all the old threads.
14. Create your own rules, ask them to be stickied.
15. Post really specific threads that no one knows about. "Who here plays Chinese dragon chess?"
16. Pretend to be an admin that used to own the forum before it got taken over.
17. Offer the admin $1,000 for the admin account.
18. Create your own index, ask members to submit there work.
19. CAPITALIZE ALL LETTERS
20. CaPiTAliZe SomE Of ThE LeTTErS
21. Make all your posts images and upload them.
22. 5P34K 71K3 TH15
23. Use tags around this: [url]http://upload.wikimedia.org/wikipedia/commons/8/8f/Whole_world_-_land_and_oceans_12000.jpg[/url]
24. Put 200 pictures of hitler in a single post, porn, or a picture of David Bowie as the goblin king with the caption "i am going to punch you in the dick" [/QUOTE]
I can't find much real info on forum spam other than this which doesn't mention laws:
[CODE]http://www.spamlaws.com/forum-spam.html[/CODE]