More poking:

(gdb) p it->glyph_row->glyphs[1][20].object
$44 = 101922033
(gdb) xtype
Lisp_String
(gdb) xstring it->glyph_row->glyphs[1][20].object
$45 = (struct Lisp_String *) 0x61334f0
  ""

(gdb) p ((struct Lisp_String *)0x61334f0)->data
$48 = (unsigned char *) 0x4fe9388 ""
(gdb) p ((struct Lisp_String *)0x61334f0)->data[0]
$49 = 238 '\356'
(gdb) p ((struct Lisp_String *)0x61334f0)->data[1]
$50 = 128 '\200'
(gdb) p ((struct Lisp_String *)0x61334f0)->data[2]
$51 = 128 '\200'
(gdb) p ((struct Lisp_String *)0x61334f0)->data[3]
$52 = 0 '\000'