Wizards of the Coast has changed its d20 System trademark license to include 'quality standards,' which include the requirement that all products bearing the d20 mark must comply with 'community standards of decency.'  Those standards are defined in the d20 System Guide as including violence and gore, sexual themes, and prejudice. 

The violence and gore standard prohibits 'art or text depicting excessively graphic violence or gore,' which is not defined. 

The sexual themes standard prohibits 'sexual situations,...the depiction of genitalia, bare female nipples, and sexual or bathroom activity.'  Clouding this prohibition is a sentence stating, 'While sensuality and sexuality may appear in a Covered Product, it must not be the focus nor can it be salacious in nature.' 

The prejudice standard prohibits depicting 'minorities, nationalities, social castes, religious groups, genders, lifestyle preferences, or people with disabilities as a group inferior to any other group.'  Furthermore, 'A Covered Product can not endorse or promote any specific religion or religious practice.'

These standards will apply to any game using the d20 logo.  WotC gives itself the right to determine at any time after publication whether the publication meets its standards; if it determines that it does not, it may require that the publication be recalled and destroyed.  With these draconian penalties, and given that there is considerable ambiguity in the standards, it is likely that they will have a 'chilling effect' on d20 publishers, who will pull back from using the d20 logo on any products that stray close to the line.