TLDR: Yes, some knives actually have safeties.
Characters switching gun safeties on and off in fiction, usually for handguns, is an easy pitfall for some writers. Not all pistols and revolvers have safeties or even hammers.
But what about knives? They don’t have safeties, right? As it turns out, some do.
Some switchblades (aka automatic knives) and assisted opening knives (similar to switchblades, but much more legal) have a small tab or screw that functions as a safety. When the knife is closed, the tab can be slipped in front of the blade, preventing it from opening.
When writing in a generic switchblade or assisted opening knife, you could ratchet up the tension by having the character switch the safety off before deploying the blade for a critical moment. You might blow some readers’ minds, but you’ll also look pretty sharp (pun definitely intended).
If you’re looking for a specific model, the Kershaw Leek (pictured above) is a popular assisted opener with a safety. Here’s a YouTube demonstration. The disembodied hand works the safety at the 15-second mark.
Get the Book
The Writer’s Guide to Weapons: A Practical Reference for Using Firearms and Knives in Fiction (Writer’s Digest Books) comes with everything but the ammo. Pick up a print or digital copy from these fine retailers: