Actually, it does show a green light when the system has processed your signal. If you send an SOS, a SAR operation will be launched.

But you are right if you mean that posting your position or sending a canned message may or may not be read and that there is no way of knowing.

(I use a SPOT on a sailboat. Does the job for me. As far as bike touring is concerned, a SPOT messenger is probably more reliable than a smartphone. Phones are more demanding battery wise, and if you travel significantly, roaming fees or local SIM cards will quickly become more expensive than a SPOT subscription)