[Zope] What is "favicon.ico" and why is it an error?

[J. Atwood]

I have a few Zope sites email me any error reports and both of the sites
(different machines) get this error about two or three times a day.

Traceback:

Traceback (innermost last):
  File /usr/local/zope/lib/python/ZPublisher/Publish.py, line 151, in
publish
  File 
/usr/local/zope/lib/python/Products/SiteAccess/ChangeBehaviors.py,line 124,
in traverse
  File /usr/local/zope/lib/python/OFS/Application.py, line 249, in
__bobo_traverse__
    (Object: ApplicationDefaultPermissions)
  File /usr/local/zope/lib/python/ZPublisher/HTTPResponse.py, line 511, in
notFoundError

As it looks for this "favicon.ico"

Anyone seen this? It is happening on two different instatallations (2.1.4,
2.1.6) on RH Linux 6.1

Thanks,
J