Stopping the rotation of a text layer parented to object oriented on path

Hi,

A simple question I imagine and I wish I'd figured it out myself! I have a tangent moving along a curve, the curve is the path and the line is oriented to the path. I then have the label "-" which I want to follow along holding its position relative to the tangent as shown. I've parented the text layer to the tangent but it is rotating as the tangent rotates. How can I get it to stay fixed with its rotation as it is at the start of the motion, the timepoint in the picture. I though with parent objects I could link the child rotation to the parent rotation using pick-whip and then add "*-1" at the end of the expression but this doesn't work.

Thanks for any help!