It spells "hoe" in a calculator if you type in "304" and flip it upside down. It's a euphemism for "whore" because you can't call women whores on YouTube or your comment is auto-removed. So to get around that people use "304" or "4TS", the latter of which means "for the streets" -- which infers that she's a prostitute -- since sometimes calling women prostitutes with negative connotations will also result in your comment being auto-removed. For content creators they also call them "304s" to avoid being demonitised for calling women whores under the hate speech/discrimination community policies.