From the National Archives: Complementing the earlier return of the mahogany table that Kennedy used to sign public laws, executive orders, and international treaties are 29 Esterbrook bill-signing pens, one used 2-fluid-ounce bottle of Sheaffer blue-black Skrip ink, and a wooden block holder with a large hole for the ink bottle and holes to hold up to 72 pens.
While Kennedy used Esters for signing his personal pen was a Mont Blanc 149. There is a photo of him loaning the pen to West German Chancellor Konrad Adenauer when he could not locate a pen to sign an official book.
Johnson used Esterbrook as well, in fact up until about ten years ago you could still order them brand new from the Johnson library. I know because I found out they were almost out and called and was the first on the waiting list should one of them fall through. Oh well, found a few after the fact, including one that was actually used to sign a bill.
I have not heard the 149 story with Kennedy, but do know he favored a Sheaffer Snorkel (Admiral perhaps, would have to dig it up). Frank Dubiel used to recall how when he was a little boy he was in a limo with his father and President Kennedy and he pulled out the Sheaffer from his suit coat. Now that being said, anyone could have used any number of pens, but I doubt during that time frame a US President would have used a German pen. Just my $.02.