The images below are only one variety of counterfeit relics. Counterfeiting relics is an ancient practice. Far from being a good sign, old relics from Europe are as likely to be fake, as they are to be authentic. The profound holiness or fame of a Saint casts immediate doubt upon the authenticity of the relic. Counterfeiters are most interested in the most famous saints. Relics of obscure Saints are more likely to be genuine. Newer Thecas (containers) that contain old saints are dubious by their very nature. Newer Saints in rusting, or old Theca's may be good sign. Old Saints in new Theca's should always be accompanied by authenticating documents. Lost papers may only mean that the documents were obviously counterfeit, and a sale is more likely to go through without the papers than with them. Older, genuine relics frequently do not have documents. There may be no way to know if an older saint, in an old Theca, with a good seal is an old counterfeit or an authentic relic.
 

The Vicarate of Rome only distributes canonized Saints. The postulators of the various orders, were charged with the cause of the canonization of a saint. Depending on the time, the postulator of the order of the Saint may  have distributed authentic relics: thus the relics will bear the seal of the particular order. The Seal of the Vicarate of Rome is not consistent from century to century, though it is similar to the above. Sometimes it has an even more square shape. While a light strike may be an attempt to cover up a poor stamp, a nice strike of the Vicarate of Rome seal is NOT indicative of an authentic relic, because counterfeiters have been much more careful to counterfeit this seal. Blackened soot marks are often present in genuine relic seals. Cracks in the sealing wax are only indicative of age. Cracks in the seal definitely can occur in larger old Thecas. 19th century Saints, or groups of Saints, with cracking seals, may be a good sign.