"And believe you me, ..."

[Odessa Dawn]

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"In short, modern Americans are a pitiful lot, ripe for the picking. And believe you me, as the low hanging fruit that we are today, we WILL BE harvested -- and soon."

Is believe you me the long form of the bare infinitive or the imperative in which we address particular people?
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[Chicken Sandwich]

***** NOT A TEACHER *****

7 believe (you) me used to emphasize that something is definitely true :
There’ll be trouble when they find out about this, believe you me!
(Longman Dictionary of Contemporary English)