The documentation says this will be returned:

"mechanicOrAgentSignature": {
"type": "driver",
"name": "driver",
"username": "driver",
"email": "driver",
"signedAt": 12535500000
},

However, all I am seeing is:

"mechanicOrAgentSignature":{
"signedAt": 1539577229078
}

This seems to be for DVIRs mechanics create via the web portal to correct defects listed by the driver.

nextDriverSignature seems to be correct
and if a driver does it via the app mechanicOrAgentSignature includes the name & username.