That may be an "inverted" S, but wait for the experts to confirm. Info can be found here: http://www.lincolncentresource.com/Featured/1946Sinverted.html
That's the MMS-006 Ball Serif in normal orientation. See this newly-published thread to confirm... http://www.lincolncentresource.net/forums/showthread.php?p=205123#post205123
Well the S looks normal (smaller on top and larger on bottom) to me, but the 6 looks more open like an inverted 9 than comparable 46-Ss shown which appear more closed. But I'm no expert on Lincolns.