They icons will only show when you are not in a 1x or digital area. Meaning if you are not in a 1x then you will see the "D" icon, and if you are not in a digital area then you will see the "A" icon for analog. You can also force the phone into those modes, but for what reason.
Hey Sunynp - Thanks for the responses. Does the 1x always mean I'm communicating through a Verizon tower?
At my old home in the mountains of North Carolina my old Samsung a310 phone got high Digital signal bars, but they'd go to zero whenever I tried to dial a number, and the calls wouldn't connect. Then, by forcing the call to analog (at only one or two bars) the calls would go through (although with annoying analog phone noise).