禁止 (jìn zhǐ) is the standard, neutral verb for 'prohibit/forbid' — used in rules, signs, and laws. It is more general than 严禁 (yán jìn 'strictly prohibit'), which is stronger and formal, and less colloquial than 不许 (bù xǔ 'not allow'), common in everyday speech. 不准 (bù zhǔn) is similar to 不许 but often appears in written rules.