I always took the word ?????? to basically mean little badge or pins. Znachki is the diminutive form of the word ????/znak or badge/insignia. The Russian mint is run by Goznak (??????????????????? or State Insignia), and they also manufacture orders and decorations, print currency, and other security related items. Znachki were collected avidly and you could get little folders full of aspecific theme. I don't know if any guide books were ever written on them per se, though I would imagine so.

Here are some Soviet era znachki, mostly with Lenin themes, that I actually got in Russia in January 1992. The Lenin ones are from the mid to late 1980s as are the other ones on the cardlabelled "Wars of Russia." The pin in the middle of the bottom row of the Lenin-themed znachki can be dated to early 1986. That piece commemorates the 27th Congress of the Communist Partyof the Soviet Union (XXVII ????? ????), notable as being the first party congress presided over by Mikhail Gorbachev, where he set the stage for perestroika. The reverse of most znachki all bear amaker's mark as well as the price - the example illustrated is the back of the 27th Party Congress pin, ?10k ("???? 10 ??????" / "price 10 kopecks").