Littlejohn joins Valiants
The 32-year-old will provide depth to The Valiants' front-line, which was in tremendous form in their 5-2 thrashing of Chesterfield on Tuesday evening.
Unfortunately, Littlejohn did not sign in time to make his debut against Queens Park Rangers on Saturday but manager Brian Horton is delighted to include the hit-man in his squad.
Horton told Port Vale's official website: "Adrian has a lot of experience and can play both wide and up front.
"I am delighted he has joined us."
Littlejohn has been looking for a club recently, having also taken a trial recently at fellow Division Two side Barnsley.