If you see forum spam for Tiffany products, note down the domain name used, then fill in the form athttp://www.tiffany.com/Customer/Request/EmailCustSvr.aspx
Select as subject "Tiffany for Business - Account Management"
Cite the domain name and let them do the take-down work.
Easy as can be.
If you contribute the reputation services loke MYWOT or SITE ADVISOR, you can also give the rogue domain name a blast there for good measure, because they deserve it.
For an example of the results, see http://tiffany68.com
You can see the esteemed spamming for this at many forums as recently as December 2014