Within the framework of a competition (i.e. ASF TRAP, SKEET), this official ISSF MARKER TAPE is mandatory. It aids the Referee in controlling the position of the gun. The tape must be permanently affixed to the shooting vest (i.e., outer garment) according to rules you may find on https://www.issf-sports.org .
 
These Marker Tapes are also sold individually or by lot of 5.