Is there a distinction between 禁止 (jìnzhǐ) and 严禁 (yánjìn), which both mean "forbid"?
严禁 is short for 严格禁止，which means strictly forbid.
禁止 is kinda suggestive，严禁 indicates something is obliged not to do by the rules or law.
Actually in everyday use, there is no obvious distinction between them.