Greetings gentlemen, is there any references showing the type of warning symbols and labels which are needed to be posted on electrical switchgear, MCC, fence of transformer/substation, etc..
It really depends what you are trying to accomplish.
For general safety signage ("Danger, Keep Out" type and specific warnings for authorized workers) I would look to ANSI Z535.2. There may be others that are applicable, but I use ANSI signage a lot. If you look hard enough, there are a couple "draft" ANSI Z535 documents out there that don't require purchase. I believe ANSI is now making old versions available for web viewing, but can't find the webpage anymore.
Here is a good, free guidance document for ANSI signage:
