It is an old word for 'poet' (maker of verses). On the other hand, some Versers are known descendants of John Vasser of Virginia, died 1635. See the book "The Descendants of John Vasser of Virginia 1635-1984, a family history." by Lyndal G. B. Vessar. My guess would be that Vasser derives from the French name Vasseur (from vavaseur, which in the feudal system was the vassal of a vassal).