there's two types of turn signals. Single screw or two-screws lens cap. Which you have?
if it's the single screw on the bottom type, just use some electrical tape on the bottom to hold the lens to the chrome shell, temporarily or semi-permanently. It ain't going anywhere as long as you clean of the surfaces well and the plastic barb at 12 o' clock on the chrome shell is still there. Actually, I put some tape there anyways just in case the tongue on the lens breaks or the screw falls off. The tape isn't visible placed on the bottom. Probably works on two screw lens but visible.
P.S. some people tape a spare screw inside the chrome shell.
