For the most part, determining whether or not a TV is an analog set or equipped to receive digital TV signals is not something that can be done by simply looking at a TV. However, it's simple to figure it out.
Identification
The easiest way to figure out if your TV gets a digital signal is to check the specifications listed in your TV's manual. If the specs say your TV is equipped with an "ATSC" tuner or receiver, "digital" tuner or receiver or "DTV" tuner or receiver, then your TV is capable of receiving and decoding digital TV signals.
Alternative
If you don't have access to your TV manual, you could contact your TV manufacturer's customer-support department to ask them if the model you own is digital ready.
Other Considerations
There is a mandate from the Federal Communications Commission in place since March 1, 2007, requiring all TV manufacturers producing TVs for sale in the United States to equip those TVs with internal digital tuners. In addition, retailers were required to prominently post notices to customers informing them about any remaining TV sets in inventory that were not digital ready. Therefore, if your TV's date of purchase was post March 2007, it very likely is equipped to pick up digital signals.
Tags: digital signals, tuner receiver, digital ready, March 2007, your manual