What does it mean an ugly pop-up with an smiley face on my lock screen? I've been getting pop-ups in the lock screen of my "Huawei Honor 6X" like this:



The notifications appear at random times. There is nothing else on the pop-up other than the smiley face made of ASCII characters and an OK button. The UI does not even look genuine. 

Any idea what does it mean or what could it be creating these messages?

It is running EMUI version 5.0.1, Android version 7.0 and Android's November 6 2017 security patch.

UPDATE: The Notification History app did not register any app producing this pop-up. Her is another screenshot of the pop-up.
I've also started getting these and can't help but notice that you are also roaming with Telcel so my best guess is that these are USSD code dialogs from Telcel, basically it looks like they're either running some tests or having fun with it