plus ("+") sign in file perms

[Evuraan::ഏവൂരാന്‍]

I've seen this mostly on hardy (coreutils ver 6.10)

$ ls -l /dev |egrep "\+"
crw-rw----+ 1 root   audio    14,  12 2008-12-26 19:15 adsp
crw-rw----+ 1 root   audio    14,   4 2008-12-26 19:15 audio
crw-rw----+ 1 root   audio    14,   3 2008-12-26 19:15 dsp
crw-rw----+ 1 root   audio    14,   0 2008-12-26 19:15 mixer
brw-rw----+ 1 root   cdrom    11,   0 2008-12-26 19:15 scd0
crw-rw----+ 1 root   audio    14,   1 2008-12-26 19:15 sequencer
crw-rw----+ 1 root   audio    14,   8 2008-12-26 19:15 sequencer2


What does the "+" sign at the end of the 1st field, eg: crw-rw----+  denote?

thx.