We can pat ourselves on the back for being popular enough to attract spammers.
How should we define spam and what should we do about it?
A typical profile of a spam user is someone who:
If it's clear that every post from a user is spam, then a moderator needs to delete their account (note: this is Stack Exchange policy). Otherwise, we give them the opportunity to change their behaviour. Leave a comment on their spam posts like:
Just a warning that spam is not welcome here. It's OK to advertise your product where it answers a question, but you must disclose that you work for the company in the post, and participate elsewhere in the site without advertising.
If there is no change in behaviour then start suspensions for 7 days, and then double that for each re-offence. Also delete all of their spam posts and/or remove the spam content from quality posts.
If you suspect spam in a post, then it's really important that you flag a moderator for the suspicious post (otherwise we might not see it). We can then perform further investigation.