Some valuable information here regarding the use of rubber stamps in your creative.  Some content below from About.com (http://rubberstamping.about.com/od/gettingstarted/g/angelcompany.htm).  If your creative uses a rubber stamp impression it is important that you research the stamp company and their Angel Policy to determine if it can be used in this manner.
 
Rubber Stamps - Angel Policy  
An Angel Policy clearly defines whether rubber stamps can be used to create products to sell. It will state whether there are any specific restrictions or limitations.
 
Most rubber stamping companies have an Angel Policy. This is a form of Limited License and states how a rubber stamped image may be used, for instance, whether it can be used to create products for sale.
 
Copyright is particularly pertinent to rubber stampers as the images replicated on stamps are typically designed by someone else. The originating artist may wish to protect their designs and how they are used. An Angel Policy is a limited license that specifies how the stamped images can be used.
 
Most Angel Policies allow the use of stamps to create hand crafted items for sale, providing that the images are hand stamped and not mechanically produced (read: digitally reproduced as in the case of PODs).  
 
The types of restrictions that a stamp company may wish to apply include:  
o Number of items made
o Places that items are sold  
o Copyright statement required  
 
Angel companies or companies with Angel Policies will define this on their website or in their catalog. If there isn't a web page headed 'Angel Policy', other places where an Angel Policy might be listed include FAQs and About Us.  
 
These policies are not designed to inhibit the creative output of stampers and in fact help protect the hand stamping business, by ensuring that stampers who want to sell their hand crafted products can do so without the fear of competing with mass produced versions of the same image. It also protects the designers ensuring that they can continue to provide a wide range of interesting and innovative designs.