Though I would never recommend on-street vigilantism, it is sometimes helpful to understand the information on a Blue Badge in case you are considering reporting potential abuse of a Badge.
New style Blue Badges have a badge "number" in the format:
aaaaaa b ccccdeeeef
aaaaaa is a unique reference for the Badge - I believe this is six randomly generated characters, but it might contain a reference to the issuing Local Authority
b is zero on my Badge - it might be the number of replacements issued
cccc is the month and year of the Badge holder's birth, so 0190 is January 1990 (or 1890 if we're going for the world age record)
d is the Badge holder's gender: X is male, Y is female
eeee is the month and year of the expiry date
f is R if the badge is reviewable on expiry (a new mobility assessment may well be required), otherwise it is blank
I think someone may need a biology lesson with the gender marker, as males are XY and females are XX. The gender marker is Badge holder's declared gender, so a transsexual's badge may be issued in the gender they are or have transitioned to.
The bar code on the back of the Badge contains ccdeeee in Code 39 format according to my scanner (the year of birth, the gender marker and the month and year of the expiry date).
It's the year of the Badge holder's birth and the gender marker that may help if you are trying to determine whether the Badge belongs to anyone in the vehicle. If you see 28Y and the Badge is being used by a young man, you know the Badge belongs to an elderly female. Don't forget that it is quite legitimate to park with a Badge so long as you are collecting the Badge holder.