We want phrases to describe suspicious not sentence

Either way may be used and is grammatically correct. "Looking suspicious" means to have a suspicious image, and "acting suspicious" means to act or behave in a suspicious manner.

Someone or something not suspicious: trustworthy or trusted.

Someone not feeling suspicious : trusting, unwary

Suspicious characters do a lot of lurking about...

The word 'suspicious' can indicate that a person is distrustful or skeptical (e.g. I was suspicious of his intentions), or that a person or situation looks a bit dodgy (His behavior was suspicious).