Sorry for the loss of your firearms.
A lot of very good suggestions to ensure a little extra safety in possible recovery.
Photos, serial numbers and makers marks would all be good ways to ID your guns.
Another suggestion is to take a pencil tracing on the gun's markings and serial numbers and then circle them with a description of where the marks are located on the guns.
You could have some hidden marks as well located out of view on the arm to make stronger verification of ownership in case of them ever coming back to you.
I hope you do get them back.
After having been through a few riots, I must admit I am tempted to leave a flask full of smokeless and a less than desirable rifle in some hot spot of illegal activity.
But you never know, with the mentality of the kind of people that would pick it up and start to load it up, they would also have the mentality to have some little kid fire it, thinking it would be funny to watch the kid get knocked down while sipping at their malt liquors, then there would be the chance of hurting a poor innocent little kid along with people who might deserve to be injured or killed in such a scenario.
Not really a pleasant thought.