During WWII, it was illegal to have icing or decorations on commercial cakes, and the attitude certainly extended to home-made cakes as well, so that many were left uniced. Personally, I usually only ice cakes for birthdays or special holidays, but this is also because I tend to eat most of the icing straight out of the bowl, along with most everyone else in the house.
Last night though, I needed to ice a cake because I had forgotten to add in the syrup that does most of the sweetening. When I went to open up my icing sugar, I found that it was nearly empty (of course), but I did manage to improvise just enough to get a thin icing out of what was left. Take 1/3 to 1/2 scant cups GF icing (confectioner’s) sugar and beat in one tablespoon of syrup from tinned fruit. I used apricot, because it went well with the cake, but you could use any flavor. Thin with a few drops of milk until you have enough to spread. Because this icing is so thin, it dries into a nice “crust” on top of the cake.