A turnpike sign is a type of road sign used to indicate the rules and regulations of a highway. The four solutions for the term 'turnpike sign' are EXIT (4 letters), MERGE (5 letters), YIELD (5 letters), and NOEXIT (6 letters). EXIT indicates that drivers should leave the highway, MERGE indicates that drivers should MERGE with traffic on the highway, YIELD indicates that drivers should give way to other vehicles, and NOEXIT indicates that drivers should not EXIT the highway.