Now I’m somewhat known for taking up lost causes. This, however, is a cause that has yet to be found! Just for verification, I’ve found two websites that reference the use of 55. You can find them at PA3BWK’s Ultimate Morse Code Website and at AC6V’s site’s Morse Code Operating Aids.
You might try it yourself in your CW and RTTY contacts. See if you can get a few people scratching their heads. It’s always good to change a few things just to mix it up.
73 and 55