What does "H" mean in the signal indicator?
Let's state all the possible letters in the signal indicator, in descending speed (indicated speeds are roughly theoretical maximum):

5G = 20 Gbps
LTE+ = 300 Mbps
LTE = Long Term Evolution (commonly and falsely known as 4G), 100 Mbps
H+ = HSDPA Plus, 10 Mbps
H = either HSDPA (3.5G) or HSPA+ (3.95G), depending on your network provider, 2 Mbps
3G = UMTS (3G), 384 kbps
E = EDGE (2.5G), 40 kbps
G = GPRS (2G), 14 kbps
(no letter) = voice only, no data connection, 2.4 kbps

and also:

R = roaming (this means you're not on your home network)

(source for some of this.)