Is this a standard representation of a 'space' character? I recently came across a handwritten note with directions to push a string of text into a database. There was a strange character in the string I've never seen before, a lower case 'b' with a forward slash through it:



I asked the author about it and he said it was an old-school way of representing a space.

My question is whether or not this was a standard/widely used representation of a space character and if so, whether or not it's still commonly used.
The symbol ␢ has a unicode representation: 2422-unicode-blank-symbol.

It is an old typographic symbol for specifying explicit blanks in code.
As Wikipedia states: 


  This was used in the early years of computer programming when writing
  on coding forms. Keypunch operators immediately recognized the symbol
  as an 'explicit space'.


ps. I also learned this symbol as Turing tape blank. I will check an old book later. Nowadays I would use B or if I am feeling adventurous ␣ 'open box' (U+2423) $\text{\textvisiblespace}$.