What is identified in the film as an "M590" is in reality a visually modified SIG-Sauer P220 Sport. The modified pistols are the sidearms carried by agents of the "Multiverse Authority" (MVA) including MVA Agent Evan Funsch (Jason Statham) and his fellow MVA Agent Harry Roedecker (Delroy Lindo). This particular handgun is modified with had a long compensator along with some futuristic weaponlight and sighting device, which is used as more of a target symbol than a point when seen on a target. Later in the film, Funsch (Jason Statham) also briefly used an even more customized version of the gun.
"Little Brother" (Modified Sphinx AT 380)
After showing off his special M590, Funsch shows the "Little Brother" of the pistol, which appears to be a modified Sphinx AT380. When his Custom Modified M590 was destroyed, Funsch pulls this backup pistol. The backup pistol can probably be surmised to have similar capabilities as the larger version, such as the ammo type and tracking modes.
LASERAIM Series III
A LASERAIM Series III .45 ACP pistol is the sidearm of LAPD officers escorting Lawless in the Anubis Universe.
Beretta 92FS
The Beretta 92FS is the sidearm carried by LA Sheriff's deputies and LAPD officers including Officer Aldrich in Gabriel Law's universe.
What appears to be a modified Heckler & Koch USP handgun is seen carried by Yulaw (Jet Li) early in the movie, but was taken away when he was caught. The pistol appears to be visually modified like the SIGs in the film.
Vektor CP-1
A two-tone Vektor CP1 is used by the guards of the MVA's universe. Yulaw (Jet Li) steals one of the pistols from a guard during his escape and notably uses it while in the hospital.
Rifles
M4A1
The M4A1 is carried by LAPD officers escorting Lawless (Jet Li), the prisoner in the Anubis Universe. The rifles are fitted with the M26 MASS in addition to C-More red dot sights and Surefire tactical flashlights.
Heckler & Koch G36K
The Heckler & Koch G36K is carried by the Los Angeles Sheriff's Department Deputies escorting the prisoner in the universe inhabited by Gabriel Law (Jet Li), aka "the Osiris Universe".
Shotguns
M26 MASS (Modular Accessory Shotgun System)
The M26 Modular Accessory Shotgun System are mounted under the M4A1 carbines carried by LAPD officers that escort Lawless in the Anubis Universe. The MASS in this film is the early version as later production models are slightly different.
Heckler & Koch FABARM
A Heckler & Koch FABARM FP6 shotgun is seen used by the LA Sheriff's Department of Gabriel's universe. Yates (Dylan Bruno) is seen trying to restrain Gabriel with the shotgun, but the weapon is bent by Gabriel.
Submachine Guns
Heckler & Koch MP5SD3 (Modified)
Two-tone submachine guns are seen in use by security forces of the MVA's universe. Judging from the weapon's handguard, these appear to be customized versions of the Heckler & Koch MP5SD3. The weapons are fitted with a chrome barrel extending at the end and fitted with chrome magazines. The stock appears to be taken from the Heckler & Koch G36.