I had a thought that these would be cool, so I looked and of course they already exist for other applications.
They work equally well on aluminum and titanium.
You really only need the higher temp sticker in the first photo, but I wasn't sure how much they would lag behind the water temp so I got both to start. Turns out it is only 5-15 degrees cold, more disparity at higher temps. And if its really windy or your pot lid doesn't have a good fit, the accuracy will suffer a little more.
It is extremely handy to be able to glance at your pot from across the campsite and know the approximate temperature of your water. Get 10 stickers here for $16: http://www.tiptemp.com/Products/TLCSEN006-Temperature-Label-7-Level-Strip-4
Hope this helps someone out!
Keegan
ps. here is a video demonstration: https://youtu.be/34MYFBZU_wc
