Remove the air tank and paintball hopper from the gun.
Clean the entire body of the gun, removing any debris or old paint that may be residing on the surface of the gun.
Examine the back of the gun's body. The majority of gun models have the serial number stamped or engraved on the upper or lower portion of the body toward the bolt.
Search the serial number on a search engine such as Yahoo! or Google. This will allow you to see if anyone online is claiming the marker is stolen.
Visit your marker's official company site if you think your marker is part of a recall. Typically, they will release the range of serial numbers of affected guns, and you can compare your number to those posted.