Weirdo code?

[Wol's lists]

I've just tried to do a cut-n-paste into a piece of music, from 
http://lilypond.org/doc/v2.19/Documentation/notation/bars

At the very bottom you'll find

\relative c' {
  c1 \mark \markup { \musicglyph "scripts.segno" }
  c1 \mark \markup { \musicglyph "scripts.coda" }
  c1 \mark \markup { \musicglyph "scripts.ufermata" }
  c1
}

Okay, I was only copying the markup bit - I wanted it as markup in the 
middle of the bar - but I had to add a # as follows:

\markup { \musicglyph #"scripts.coda" }

Looking at the code behind the web page, it looks like that is correct, 
so this is really just a curious enquiry - why is the # required if I 
want a markup, but it's not required if it's a markup within a mark ???

Cheers,
Wol