The Collaborative International Dictionary of English v.0.48:
Guidepost \Guide"post`\, n. A post at the fork of a road, with a guideboard on it, to direct travelers. [1913 Webster]WordNet (r) 3.0 (2006):
guidepost n 1: a rule or principle that provides guidance to appropriate behavior [syn: guidepost, guideline, rule of thumb] 2: a post bearing a sign that gives directions or shows the way [syn: signpost, guidepost]