As seen on the Site Directory and on the respective sites, here are:
The icons for Physics:
physics touch icon http://sstatic.net/physics/img/apple-touch-icon.png physics icon http://stackexchange.com/images/icon/physics.stackexchange.com physics favicon http://sstatic.net/physics/img/favicon.ico
(from http://sstatic.net/physics/img/apple-touch-icon.png, http://stackexchange.com/images/icon/physics.stackexchange.com, and http://sstatic.net/physics/img/favicon.ico)
The icons for Parenting:
parenting touch icon http://sstatic.net/parenting/img/apple-touch-icon.png parenting icon http://stackexchange.com/images/icon/parenting.stackexchange.com parenting favicon http://sstatic.net/parenting/img/favicon.ico
(from http://sstatic.net/parenting/img/apple-touch-icon.png, http://stackexchange.com/images/icon/parenting.stackexchange.com, and http://sstatic.net/parenting/img/favicon.ico)
I know that Physics had its own custom logo for a short time, and will someday get a replacement. And I know that Parenting is likely to launch later this year, at which point it will get its own logo.
But for right now, it's confusing—and that's not even taking into account that (theoretically) Philosophy could go into beta.
Could these be made unique in some fashion?