Likewise, not all numismatists collect coins themselves. Often called professional numismatists, they authenticate or grade coins for commercial purposes. These coins are also known to numismatists as holey dollars as well. It is believed by numismatists that these coins were fractions of a shekel. Postal orders are gaining in popularity as collectibles, especially among numismatists who collect banknotes. Numismatists took little interest in the coin. The charts numismatists produce to represent the production of coins are bipartite graphs. To numismatists, Green is known for his extensive coin collection. The coins are also known to numismatists as "thrymsas". Among numismatists, the modern carvings already greatly outnumber the classic old hobo nickels. Today, the stolen banknotes are a collectible for numismatists. This obverse had been termed the "No Shoulder Strap" variety by numismatists. All fifteen extant specimens are acknowledged and studied by numismatists. Eagerly collected by numismatists today, they are among the most valuable Lincoln cents. Exceptions were allowed for numismatists, jewelry makers, and normal tourism demands.