No idea what “Syntra” is in this context. It could be a reference to a crew member: on other props there is mark ups for “boyd gak”; Boyd I believe is the name of a propsmen, and gak is the nondescript design bits and pieces that covers the props to make them look more interesting. So Boyd Gak is the gak crafted by Boyd.

I’ve seen it spelled “Sintra”, but it’s clear acrylic used frequently in prop making.