I was looking to find some example carbon star spectra and came across this page on the Harvard website which shows several plots of carbon star spectra. The horizontal axis is labelled as wavelength in ångströms, but the vertical axis appears to be labelled with "g-98" which I am not familiar with - any idea what quantity this is?
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 email@example.com 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!)