Do I need synchronizer block for this

The reason for the feedback is to clear the flag in the fast clock domain to look for more pulses. If you will only have one ever between resets, your code should work fine. If you have multiple pulses, you need a way to clear SigAFlag in your fast domain.

I have seen recommendations to use two registers to cross clock domains. Although it may be bad practice, I have always used one and had no real issues with it. Using two shouldn't be a problem, it will just take a little more time and a few more resources. Good luck with your design!