The railroad crossing warning sign called a crossbuck is shaped like this letter
Familiarity with symbols on traffic signs is important for every road user in ... Sign 
shape can also alert roadway users to the type of information .... and Light Rail 
Transit Grade Crossing Sign "RAILROAD CROSSBUCK (R15-1)... [DOC] [TLE] Glossary | Operation Lifesaver, Inc. [PAR] Constant Warning Time - A motion sensing system with the capability of 
measuring train speed and ...