The Stack Overflow guidelines under Help center > Our Model specifically state the following:
The community tends to vote down overt self-promotion and flag it as spam. Post good, relevant answers, and if some (but not all) happen to be about your product or website, that’s okay. However, you must disclose your affiliation in your answers.
If a large percentage of your posts include a mention of your product or website, you're probably here for the wrong reasons. Our advertising rates are quite reasonable; contact our ad sales team for details. We also offer free community promotion ads for open source projects and non-profit organizations.
We have at least one user here at Photography.SE that includes links to their own website in practically every answer that user has posted here. This user never discloses that the links are to that user's own website.
I've flagged a number of them for moderator attention, and yet nothing seems to ever be done.
Are specific communities at SE allowed to blatantly disregard the core guidelines of the entire SE network?