Retraction Watch is a blog produced by Ivan Oransky and Adam Marcus and was launched in August 2010. The blog reports on retractions of scientific papers and on related topics. Retraction Watch was created to increase the transparency of the retraction process.
The founders observed that:
retractions of papers are generally not announced,
the reasons for retractions are not publicized
researchers or the public who are unaware of the retraction may make decisions based on invalid results.
Third Iron (Browzine) has incorporated Retraction Watch data into the LibKey linking algorithm. Now, researchers are notified at the point of discovery when an article has been retracted, plus given additional details about why, regardless of whether retraction is indicated by the index or publisher!
For researchers starting at websites like PubMed, the LibKey Nomad browser extension clearly labels articles as retracted.