The letter followed complaints that campaign signs had been posted more than a week ago by candidate David Miller.
"It has been reported that there are isolated sightings of campaign signs on some residential and commercial properties throughout the city," Fialho said in a letter sent March 5 to the four council candidates.
In addition to Miller, others seeking the vacant council seat are Mark Hamilton, Kathy Narum and Olivia Sanwong.
"I would like to call your attention to the established commencement time for displaying campaign signs, Friday, March 29, which is 40 days prior to the election," Fialho wrote.
"While this requirement is voluntary, we have found that local candidates have historically complied with this standard for the benefit of the community. I'm hopeful that all of you will do the same," he added.
Fialho said that the city has found that the 40-day timeframe limits complaints from the community regarding "sign blight" and narrows the time in which city code enforcement is required to follow up on improper placement of signs on public rights of way.