All the of the preceding comments are accurate, but you didn't mention what models or calibers, so I wanted to add some info peculiar to these rifles because of there association with the middle east countries.
You are probably seeing various versions on the internet with all sorts of descriptions and markings that can be confusing.
To begin with, quite a few are BOGUS mid eastern copies. Some were re-worked in the early 20th century and so marked. I.E. "CITADEL 1901" or whatever.
Authentic UK made Martinis will have the royal cypher of Queen Victoria, the factory of origin, and the date of manufacture stamped on the RH side of the receiver.
They could have been made by B.S.A., Enfield, L.S.A., and perhaps other subcontractors.
I believe most original Martinis were all made well before 1898.
Judging from their scarcity, not many were sent back to the arsenals at the end of the 19th century to be re-fitted with .303 barrels. Of the ones I've seen, they were stamped on the LH side of the receiver in similar fashion as the RH, but with the .303 caliber designation added as well as the "reman" date ; and that could be anywhere from possibly 1896 to perhaps 1901.I have only seen 1898 and 1899 myself.
So, I would say most of the dated Martinis are antiques.But technically, .303's may be considered modern because of ammo availability regardless of the date.
To avoid fakes,you really have to study AUTHENTIC Martinis to judge the markings on specimens offered for sale.
Queen Victoria died around 1899, so any rifles built at the arsenals after that date would have her successor's cypher.That amounts to a different style crown and some other details and later dates. Luckily, most fakers are not historians, so you will see dates as late as 1914 stamped on a gun with a crude Queen Victoria cypher.
Bottom line, I'd be more worried about buying junk than an antique !!