>WARNING!< This is an amateur's interpretation of 110.21(b)(1)!
If it is legible, and (as suggested) follows 110.21(b)(1) "using effective words, colors, & symbols..."
The informational note points to an ANSI standard for those effective words, colors, & symbols.
You mentioned stencils-- you'd probably need at least 2-- one for red or yellow, another for black lettering. You might need to spray the area for the warning with white before you start on the warning labels. Black lettering on a dark grey cabinet is not very legible!
Might be easier to check out one of the commercial office supply catalogs-- they might have the right sign available in a peel-and-stick version.