Police are probing comments and images posted on the website of the Vanguard Bears.
It has since emerged that the group is kit sponsor of Rangers starlet Robbie Crawford.
The website contains photos of prominent Celtic fans, some dead, with crosses superimposed on to the images.
A Rangers spokesman said: "The club is investigating."
The photos include one of the late Paul McBride QC and another of lawyer Paul McConville, who died last month.
A Police spokeswoman said: "We are looking into the matter."