This isn't necessarily insulator related, but I have faith that someone here will know the answer. While traveling around Ohio, I always see these little triangular markers on utility poles, traffic sign posts, trees, guardrails, and sometimes on their own dedicated steel post. I assume they have something to do with underground utilities, but can find no information about them anywhere. Does anyone know what they are? Thanks.

UPDATE: They denote underground utilities. Blue = potable water; Orange = communications lines