WOW I have been on AT&T for a long time and have never seen that before. Also my daughter was there and her phone did not have that either, only mine.
Ok I have checked the site you gave, but this is not over by the signal strength, it is by the AT&T.
"Roaming indicator. Indicates that the device is roaming. If the roaming indicator appears beside the network type (such as GSM, GPRS), you are roaming into another wireless network coverage area the is not part of your home network."
Realize that the roaming indicator can be moved to a different location. With that said, it does not look like the roaming indicator I see in theme builder.
i posted this last week or so. its the wifi roaming indicator. it appeared on my tmo branded 8900 on at&t after i switched to .314. its actually a UMA related icon that turns green when you are connected to your home wifi network. do you have a tmobile 8900 on at&t?