Avatars are supposed to be a fun thing. Do not use them for controversial political or other controversial topics. Do not use them to promote illegal activities. A blatantly pro-drug avatar is probably going to run afoul of the illegal activities rule.
There is a bit of ambiguity in current drug laws, especially with regard to cannabis, where states have legalized its use but usage remains illegal at the federal level. The guideline here is that you can do whatever would not get you in trouble if you did it in front of a police officer in Chicago (where the SDMB is based).
That said, we have enough problems here with folks thinking that “dope” in our name refers to drug use, and content related to drugs here on the SDMB can result in the site getting listed as a “drug” site and blocked by many filters, and also lowers our ranking on search engines. We would appreciate it if everyone avoided such topics as it has the potential to negatively impact traffic coming to our site, which our survival depends on. Don’t bite the hand that feeds you, folks.
If you want to take a pro-drug stance, there really are better places on the net than here that you can do so.