Are you still responsible for the total signing bonus over the remainder of the contract if you trade a player?
I haven't tested this. Was curious if anyone knows.

Yes

And if they retire.

You are always responsible for the bonus, no matter what.

Thanks guys

If you trade a guy with 4 million in bonus spread out over the next 4 years, does the 4 million all hit your current years salary cap?

After having the trade accepted it looks like the answer is the current year bonus hits you this year, and the remaining hits the next season.

I wish it was all this season.

Yes. Trades accelerate the bonus. Current yr bonus goes against current dead cap. All remaining bonus for all years accelerate to dead cap next year.