Whenever you feel the need for a safety sign that is ANSI Z535-compliant, just use the Safety Sign Generator. Pick a level of warning with a signal word, select a pictogram or two, and write out any kind of notice you wish.
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The examples here were generated by commenters at Metafilter. There are a ton of them if you need a laugh or some inspiration, although some are hilariously rude. Damon Burke, who designed the generator, also has one for Laboratory Door Safety Signs. Go wild with both of these!