Nothing that I'm aware of. The goal for all drawings is to achieve consistent, unambiguous clarity and minimize confusion.
Different companies use different "flags". The company I'm currently with prefers the upright ('point' upward) equilateral triangle. Some rotate that same triangle 90 deg CW ('point' to the right), others use a hex or a five sided flag (somewhat pennant shaped).
The square can be confused with other symbols or notations such as note outlines (which some companies use), basic dimensions (esp. on metric drawings) or even the square symbol that preceeds a dimension (sometimes used in GD&T).