The little directional arrows that are on all NFL fields, next to the 40, 30, 20, 10 yard numerals, and point to the closest end zone. Believe it or not, they are regulated by the NFL, as to the size - it is standard on all the fields.
What is this size?
I hope I've worded this question, so you can understand it, but if not, here is some additional wording which may confuse you more, or help you some.
Each arrow is a triangle. The two longer sides, point to the goal lines, and are the same length. The shorter side, runs parallel to the yard lines.