personalSign.js

const ethUtil = require("ethereumjs-util");
function personalSign(privateKey, msgParams) {
    var message = ethUtil.toBuffer(msgParams.data)
    var msgHash = ethUtil.hashPersonalMessage(message)
    var sig = ethUtil.ecsign(msgHash, privateKey)
    var serialized = ethUtil.bufferToHex(this.concatSig(sig.v, sig.r, sig.s))
    return serialized
}
function concatSig(v, r, s) {
    const rSig = ethUtil.fromSigned(r)
    const sSig = ethUtil.fromSigned(s)
    const vSig = ethUtil.bufferToInt(v)
    const rStr = padWithZeroes(ethUtil.toUnsigned(rSig).toString('hex'), 64)
    const sStr = padWithZeroes(ethUtil.toUnsigned(sSig).toString('hex'), 64)
    const vStr = ethUtil.stripHexPrefix(ethUtil.intToHex(vSig));
    return ethUtil.addHexPrefix(rStr.concat(sStr, vStr)).toString('hex')
}
function padWithZeroes (number, length) {
  var myString = '' + number
  while (myString.length < length) {
    myString = '0' + myString
  }
  return myString
}


const privKeyHex = '4af1bceebf7f3634ec3cff8a2c38e51178d5d4ce585c52d6043e5e2cc3418bb0'
const privKey = new Buffer(privKeyHex, 'hex')
const sig = personalSign(privKey, { data: "terms" })
console.log(`signature: ${sig}`);

https://github.com/ethereumjs/ethereumjs-util/blob/master/index.js