ESD labels are covered under MIL-STD-129.
See, in particular, section 5.2.20 of this standard. This specifies the need mark all unit packs, intermediate and exterior containers of ESD sensitive devices (or other electronic items that are alone or are part of assemblies) that are susceptible to damage from ESD.
There are two different types of ESD labels required by MIL-STD-129. See as follows:
• Unit Pack ESD Labels:
All unit packs shall be marked with the ESD sensitive device attention label prescribed by ASTM D 5445. The label shall include the ESD sensitive device symbol (triangle and reaching hand), the words 'ATTENTION STATIC SENSITIVE DEVICES' and the statement 'HANDLE ONLY AT STATIC SAFE WORK STATIONS.' The symbol and lettering on the label shall be marked in black on a yellow background. Unit packs that are not over packed and are used as exterior containers shall be marked with the unit pack label.
• Intermediate and Exterior Container ESD Labels:
Intermediate and exterior containers shall be marked with the ESD sensitive devices attention label. The ESD sensitive devices symbol and the words 'ATTENTION OBSERVE PRECAUTIONS FOR HANDLING ELECTROSTATIC DISCHARGE SENSITIVE DEVICES' shall be marked in black on a yellow background. A 2" x 2" ESD label shall be placed on the identification-marked side of an intermediate container. Then, two 4" x 4" ESD labels shall be placed on each exterior container that exceeds one-half cubic foot. One label shall be placed on the identification-marked side (or surface), and one label shall be placed on the opposite side (or surface).
Smaller exterior containers shall be marked in the same manner except that the 2-inch by 2-inch label may be used in lieu of the larger label.
If the ESD labels are temporarily unavailable, intermediate and and exterior containers shall be marked with ESD sensitive devices symbol and the information printed on the ESD labels above. The minimum size of the symbol shall be 5/8" (measured vertically at the base of the triangle). When preprinted ESD labels are not used, the symbol shall be printed in black or the same color as the identification markings, if other than black.