The sign was mounted on a bright yellow bike in Arnside and marked a turning point on the route at the end of Milnthorpe Road.
Morecambe Bay Partnership had offered a reward for the return of the bike.
Twitter user David Miller tweeted on July 5: “I hope whoever has taken the yellow #morecambebaycycleway bike from its vantage spot has a real bad day.”
On July 6 he tweeted: “The scallywags conscience was too heavy a burden to carry, and so was the bike!”