Check this compiled list of various ideas as to what the acronym
S.P.A.M. means. The official meaning of SPAM in terms of the Internet
is
"Self Promotional Advertising Message".

But here is a list of alternatives that some people have come up with:

Stupid Posts Are Meaningless

Stop Posting Annoying Messages

Single Posting Addressed Multiple times

Stupid People Are Mandatory

Suckers Protesting Against Midas

Stupid Pricks Are Annoying Me

Seriously Poor And Mean

Some People Are Morons

Stupid Person At Machine

Stupid Phucker At Machine

Simply Put, Advertising Motherfuckers

Stupid Posters Advocating Maliciousness

Sexual Perverts And Moneygrabbers

Sad Person After Money

Stupid People Asking for Money
(Usually seen in the fast & free.money newsgroups)

Or if referring to the meat related product
Some Parts Are Meat
SPiced hAM *
SPreadable hAM *
Suspicious Pinkish Adulterated Meat
Spoiled Pork And Meat
Squirrels, Possums And Mice
Strangled Parakeets and Animal Manure
Several People's Amputated Members
Satan Posing As Meat
Seventy Percent Anaemic Marsupial