As far as I know, the authorities are aware of the activities of hucksters with a large turnover. From time to time they are covered "for show", and of course they pay a certain fee. Bookmarks are mainly done by sellers working on the Internet, on thematic forums that are not located on the servers of other countries, where it seems that they are not in danger by law. In any case, it is not profitable for the authorities to deal with sellers, because they are far from the most important in the hierarchy of their business, and from the point of view of combating drug addiction, this is futile, because after closing one huckster, a new one will appear, especially given the current sad tendency of use among young people. There is a demand - there is also a supply, so if this seller is not some Escobar of our time, then there is no point in even trying.
By the way, sellers themselves rarely leave bookmarks, usually they are specially hired couriers, but they are usually found either on an obvious tip, or during their work. But even if they find him, they are very unlikely to come to the top.
In fact, it makes no sense to contact the police. The FSKN also knows how to install a torus. also knows the addresses of the necessary sites, and is itself capable of tracking bookmarks, and the suppliers that are of interest to them. If the tab contains a gram of hashish, three stamps, five wheels, then by handing it over to the authorities you will not make anyone better. Drug addicts will not stop being drug addicts, they will simply lose a little money, get angry, and then most likely order more. Take a bottle of vodka from the drunk and see if he will recover from alcoholism, or he will crawl for a stash. The problem of drug addiction must be addressed from the other end. Organs from these sprinkles also benefit a little. Most likely, they will just take it all, say thank you, and use it themselves (or throw it out if they are principled). This will end the matter. If we are talking about a kilogram of cocaine, then in general it is better not to touch it - as if not to get into a batch (and it can come out serious).
In any case, it's better not to touch. This is not your world, you do not know its laws and regulations. Why climb?
You can report to the police or ignore the find. It all depends on your inner beliefs. What guarantees do you need and why? Not quite clear. If you have any reasonable suspicions of police involvement in drug trafficking, please report it to the prosecutor's office.