Authentic World War One 1897 trench guns will have:

Serial number between E613,000 and E705,000
High quality rust blue finish
Solid frame
20-inch cylinder bore barrel (with no bead)
Muzzle in lone with bayonet lug
Handguard with six rows of holes
Bayonet lug with a bead sight and either "PAT APPY FOR" on the right or patent dates on the right
Stock with a thin wrist, high comb, no fluting, and no stamps
Hard plastic commercial buttplate
Sling swivel on stock

Authentic World War Two 1897 trench guns will have:

Serial number between 921,300 and 986,300 (but most between 930,000 and 953,000)
High quality commercial blue finish
Takedown frame with "U.S." and (usually) flaming bomb stamp
20-inch cylinder bore barrel (with no bead) with flaming bomb stamp on top of chamber
Muzzle extending approximately 1/4" beyond bayonet lug
Handguard with four rows of holes (except some very early ones with WW1-type heat shields)
Bayonet lug with a bead sight and patent dates on the right
Stock with a thick wrist, low comb, flutes, and inspection stamp (either WB or GHD) with crossed cannons
Hard plastic commercial buttplate
Sling swivel on stock