Accredited Blocking Notation
... It seems like you are after some ISO/OTHER STANDARDS ORGANISATION code for blocking. I can tell you now, there isn't one.
In fact, blocking often does not even involve drawing on a plan (depends on the method you prefer). For example, I was taught to put my blocking in words: (example, two characters, Ashley and Terry, there is a table DSP and USOP (Down Stage Prompt (stage left) and Up Stage Opposite Prompt (stage right)), labeled T1 and T2 respectively (on my floor plan).
(1) T -> DSOP/T1
(2) A -> DSP/T1
(3) T hugs A @ DSC/T1
(4) A -> DSP
(5) T -> 2DSP/T1
(6) A exits USP
Which is basically short hand for
Terry crosses to the Down Stage Opposite Prompt corner of Table 1
Ashley crosses to the Down Stage Prompt corner of Table 1
Terry Hugs Ashley, in the middle of the Down Stage end of the table (ie they step together and embrace)
Ashley crosses to Down Stage Prompt (no location defined, so it is relative to the stage)
Terry takes two steps Down Stage Prompt of Table 1
Ashley Exits Up Stage Prompt.
That is the method I use, which could be entirely different to what other people use.
The Stage Management world does not recognise any official standards when it comes to prompt copies, as they are a rather personal thing. There are "de facto standards" - unofficial, but widely used, like the use of Stand By and Go when cuing, but there is no "ISO1100221 - Standard notations for the creation of a theatrical prompt copy" or "ANSI29992 - Standard for theatrical cuing and show control".