If you want very formal written English, there should be a comma between "Bow Tie" and "keep"; and there should be an exclamation mark at the end of the whole sentence. But now they're playing with slogan, they could say anything la.
That is just a slogan / phase. It doesn't have to follow a formal sentense struction.
People say "Bow Tie, Fxck you". They won't say "Bow Tie !! I Fxck you."
英語中的指令句,又稱「imperatives」,根據英國 文化協會係網站上的文法解說,通常係指示別人應該做什麼、發出指示或建議,例如「Come in and sit down, please」等。這種句式較少有主詞,但有時為咗清晰說明邊個係說話對象,有時都會加上名詞,例如「Mary come here - everybody else stay where you are」、「Somebody answer the phone」。
睇完英國文化協會的解釋和例句,誰是誰非都應該好清楚。不過,煲呔喺下午傳媒吹風會上,就改咗個質疑,繼續話嗰句文法有誤,話如果唔加標點,全句應該改為「Bow Tie Keeps His Election Promise」,意思係肯定佢履行咗選舉承諾,如果係想鬧佢,就應該寫成「Bow Tie, Keep Your Election Promise」。