After posting the photo above of 105, I noted that there's a string running lengthways along the top of the aft canopy. Presumably to provide both a means to keep the blackout curtain up and to assist in drawing the curtain forward and back (though former RIO, Jan Jacobs informed me once that it (the curtain) "Didn't last long. Would come forward on a trap, plus it was just a general pain-in-the-ass to move forward and back")
A couple more photos that show this string (the second photo comes from an accident report from my collection, the ejection seat is out of its normal position as it broke loose and moved forward during the crash landing)