Forgeries of the Denikin stamps exist, as Dr Ceresa confirmed in his Handbooks, but they are very rare. For a long time, I identified them from the gum. As with most genuine Denikins (though not all), the gum on the forgeries is thick and brown. But it is smooth and varnish like - the gum on the genuine stamps is full of lumps, particles and what looks like dirt. It's very uneven and you would not want to lick it.
For a long time I could not find anything on the front which told me that a stamp was a Forgery. There is something wrong with the ornaments - the shading is too light - but that hardly distnguishes them from lightly printed genuine stamps. And St George, his horse and the dragon in the middle don't look quite right, but that could just be inking or wear. IN other words, these Forgeries are really very good copies and the colours are almost exact copies.
But today, for the rouble values, I think I have found a feature which can be used to sort the genuine from the (very rare) forgeries. It's St George's lance. On the genuine stamps,it touches the edge of the coloured oval and on the Forgery it doesn't. I have chosen the dark coloured centres of the 3 rouble to illustrate my point - the Forgery is on the right: