If you have the dodgy daves license (10milion) you have the option to search players (just like police do) and to take thing from them (backpack/back) so you can take guns/clothing etc. Very nice
Although your question has already been briefly answered by the helpful people above, I am going to go into some depth regarding the situation in case you require it.
After accumulating £10,000,000 on the server a rebel can purchase the 'Dodgy Dave's' licence which allows them to have the ability to 'pat down' players for their items. Furthermore, it allows them to search and remove players items from their backpacks. Alternatively, police get access to this feature as a way of removing a GPS off of a rebel as some of them refuse the drop them into the vehicle. In case you are wondering, the Dodgy Dave's shop is located on the South Peninsula of Altis; I recommend having at least 15 million before thinking about purchasing such a high priced licence though.
@xmas the dodgy dave's license also gives you access to high tier weaponry, for example MK-I, Type-115, Lim-85, AK-12 and more cool weapons and attachments.