What is "g-98" in plots of stellar spectra?
It looks like the floating "g-98" is just an extension of the header of the plot (made by IRAF), which has wrapped around the image for lack of room on the right-hand side. Looking at the N0 plot, we see that the header should read

NOAO/IRAF V2.10.4EXPORT perry@sparky.sao.arizona.edu Mon 06:04:51 03-Aug-98


which just contains information about the software, user and creation date behind the plot.

(Hat tip to Pela for confirming my guess!)