Let's review, and make a few reasonable assumptions as we go.
The poster "remoted into a public workstation to work on it". His/her profile indicates he/she is in technical support, so presumably he/she is authorized to take this action. No problem so far.
The poster notices that the "user is logged into personal email and viewing explicit emails". Determining the user was using this machine for personal e-mails in one thing, actually reviewing those e-mails and concluding they were of an explicit nature is quite another. Hear that crackling sound? That's the sound of the thin ice the poster is skating on here.
The poster indicates that the user was on "a public workstation, in a public area, not intended for personal use and the policy is that we do not use any PC, public or private, to view explicit content of any kind". I doubt this is entirely true, or if this is in fact corporate policy it's poorly stated and appears to be poorly executed. If the workstations are for public use and in public areas, then the part about no personal use is inconsistent. If the company is worried about the nature of the content they can simply block access to just about anything and prevent the problem from occurring in the first place.
The poster's motives are also perhaps a little less than entirely noble, because he/she is concerned that "there could be some backlash for me" and he/she wonders if it would be a good idea to "just call my co-workers over to my cube for a good laugh at how stupid and nasty this pervert is". Do the right thing for the right reasons, or do nothing.
Which, in this case, is the right thing to do...nothing. My read on this is that the poster overstepped his/her bounds, may have a little touch of vigilantism or a hero fantasy, doesn't understand the corporate policy nor the tenets of professional behavior, and would best serve the organization by figuring out a more effective way to lock down the public access machines.
The whistleblower laws? Surely you jest.