Leather Harness

I think you may be over-analyzing the issue, myself - but if you have doubts about the perception, I have a couple suggestions:

Have your hamster character wear this harness over a tropical print sports shirt, as opposed to "bare" fur. I've never seen a picture ANYWHERE, where the LeatherMan or BDSM regailia restraints and harness aren't worn against bare skin, or over tight leathers. The incongruity of a bright, open tropical hawaiian shirt will dispell any such association.

For that matter - remake your harness with colored nylon web-style belts or straps, using any color EXCEPT black, and using the vertical-horizontal assembly of straps or belts is friendlier than diagonal, criss-cross, chrome-ring coupled; also avoid ring cinches, use buckles or pull straps. This should further cloud any associations with bondage gear of any sort.

If you only have leather, try brown or rawhide, rather than finished black, and again avoid diagonal orientations, stick to right angles, with vertical and horizontal orientations.

I agree with Vulpes's suggestions, and I think you've got the right idea with buttons and badges attached to the harness- that will help it look practical. I think it's good that you're concerned about public perception of the costume, but I doubt that it's going to be perceived as particularly kinky, especially as people notice the fins and jaws, and sort of get "ohhh. Hamstershark'.

And, quite honestly, if one or two people out of the three thousand go "Huh. Bondage hamstershark." Instead of "Huh. Hamstershark.", then it's really not a big deal. Don't fret much over it!

Speaking as a con security guy: if it doesn't involved near-nudity or a collar and leash with someone else holding the leash, I think you're good to go. Collar and leash are explicitly banned, as is nudity as costume. Beyond that, we use our discretion.