dragon's teeth

Short definition from Wiktionary

Noun

1. 1
   Square-pyramidal fortifications of reinforced concrete to impede the movement of tanks and mechanised infantry.
2. 2
   A series of triangular road surface markings painted on each side of a traffic lane, used for traffic calming or to alert drivers to a speed limit.
3. 3
   Lotus maritimus, a plant in the legume family.
4. 4
   Used other than figuratively or idiomatically: see dragon, tooth.