I could tell from their headshakes that they didn't believe me.
Examples of headshake
headshake
Frenchmen examined their handiwork with a national headshake of disbelief.
From the time.com
Until he compounded his stand-up protest with a headshake that lasted all the way to the boundary.
From the independent.co.uk
Most references to the war bring a doleful shrug or headshake.
From the time.com
Either occurrence was a signal to raise the rod tip and feel the sudden, hard headshake of a hooked fish.
From the freep.com
More examples
The act of turning your head left and right to signify denial or disbelief or bemusement; "I could tell from their headshakes that they didn't believe me"
Headshaking is a condition where the horse or pony shakes its head continuously, often while being ridden.
Phenomenon where the front end and handle bars shake from side to side