This is called the Ciphering Indication Feature and some older phones did notify you when encryption was disabled.



Nowadays, however, it's useless because both A5/1 and A5/2 are breakable with an off-the-shelf PC in under a minute.

This means that GSM is ineffective in terms of security, one needs to upgrade to UMTS.

I don't know what LTE brings to the table, if anything, when it comes to security.