In chapter 4, Edgar Allan Poe, going by the name of Mr. Dupin, finds a note has been slipped into Edmund's tenement flat. The note is intended for Mr. Dupin and reads "MEDDLE AT YOUR PERIL!" (p. 39). To meddle is to interfere. The word peril means the same thing as the word danger and is used to refer to anything that can cause any form of serious injury or even death. Therefore, the message is warning Dupin that his interference could cost him serious injury or death. Later, Poe figures out exactly who had delivered the message and why.
By chapter 16, Edmund and Poe see a bill posted in the saloon that offers a financial reward to any person who has information on the whereabouts of Mrs. G. Rachett, Edmund's mother, and Poe figures out that Edmund's Aunty Pru posted the notice as soon as she reached Providence in search of Edmund's mother. Poe then figures out that Mr. Throck, a policeman of the Providence Night Watch, wrote the message because he is interested in solving the case himself he knows Poe is working on because Throck wants the reward money involved. Soon enough, Throck confesses to having written the warning message to Poe because Throck had been working with Edmund's aunt, up until she had been found dead at the docks, to find Mrs. Ratchett and still hopes to earn the reward money.