I understand that @ suppresses printing of a command in a Makefile...

http://www.gnu.org/software/make/manual/make.html#Echoing

... and I understand that $@ is the target name...

http://www.gnu.org/software/make/manual/make.html#Automatic-Variables

... but I can't find any information on what a line like this might mean:

variable=@value@

I'm not trying to fix anything here, just trying to better understand Makefiles.

Update: The "Makefile Subsitutions" section of the GNU autoconf manual explains that it's a value that is substituted by autoconf.