Hi guys! I was looking at this photo and noticed the diagonal line running from the rear bottom corner of the canopy back towards the wing root. Reading about this wreck on the 'Aircrew Remembrance Society' website, I learned that this was Gunther Bode's machine, shot down on 9 September 1940. They said it had this red line that 'was becoming common on aircraft of this period'. I've never seen anything like it, but I'm sure somebody on here would know a bit more about it?
The only thing I can think of is that maybe it was for reference by other aircraft when doing formation dive bombing? But it was only on the left side of the fuselage and the machine had no bomb rack fitted and as far as I know September 1940 was before the luftwaffe started using Bf109s in this role?