Never heard of such thing

I’m sure what they are doing is legal, but I would leave the company if I were you. Sounds like toxic management

First of all - what exactly are you referring to?

Annual performance bonus, or SIGN ON bonus? Both are 2 different things.

Anyway, like one dude earlier said - depends on what you sign on your employment contract. If it’s in there, and you’ve signed and accepted it, then too bad lo.

What the clause in the letter that you sign? Signing/ Sign In / Sign On Bonus is an incentive for employee joining a company. Normally come with clause for duration of work. Some give upfront and some give after you completed the duration.

yes. in the west this is how it works. often its only for positions that are highly sought after / competitive and with start up company where they dont have alot of funds to begin with so they will offer to give you this and that package.
but if they offer sign on bonus then either you are in a niche industry that they really want or you have a big dick that they want. either way, they want you thats why they give sign on bonus
but the stipulation usually is if you leave then you have to give it back thats why alot of people force themselves to stay for at least 1 year before the jump ship
silicon valley is notorious for this kind of hiring style