The MX 6.5 mm (Black) is missing the manufacturer information found on the regular MX 6.5 mm rifle
The issue is only found on the MX 6.5 mm (Black) and the MX 3GL 6.5 mm (Black)
Normal manufacturer markings on the MX SW 6.5 mm (Black)
Likewise for the MXM 6.5 mm (Black)
As well as the MXC 6.5 mm (Black)

This issue has been present since the introduction of the Black MX rifle family towards the end of the Arma 3 Alpha.