I have a developer edition and have used it on both AT&T and T-Mobile, and this is perfectly normal behavior for the non-carrier variants of the One. On the unlocked/dev edition Ones, here's how the signal icons should read from least to greatest signal speed:
X (no signal)
G (no data)
E (EDGE, 2G data)
3G
H (HSPA(+), considered "4G" on most carriers)
LTE
You won't get any of the carrier-specific 4G LTE icons because none of the carrier software is on the phone, just the "stock" ones. If you're showing LTE above the two arrows next to the signal bars, you're getting the same LTE as the carrier-branded Ones from whichever carrier you're using.
X (no signal)
G (no data)
E (EDGE, 2G data)
3G
H (HSPA(+), considered "4G" on most carriers)
LTE
You won't get any of the carrier-specific 4G LTE icons because none of the carrier software is on the phone, just the "stock" ones. If you're showing LTE above the two arrows next to the signal bars, you're getting the same LTE as the carrier-branded Ones from whichever carrier you're using.