Chances are, most of us don't pay much attention to the raised pavement reflectors lining the streets during our daily commutes, except maybe as a bumpy wake-up call that we're starting to drift into another lane. 

But have you ever seen a lone, shiny, blue light in the street and wondered "what's that doing there?"

I have, and this is what it means. 

The blue raised pavement markers, or RPMs, are installed by local and state agencies to assist first responders in locating fire hydrants. They are not legally required, but are encouraged as a public safety supplement. 

"Rapid location of fire hydrants can be hindered by shrubbery or parked vehicles blocking the view from fire apparatus on the traveled way," the Florida Department of Transportation's Traffic Engineering Manual states. "These markers are not traffic control devices but are a significant aid to public safety."

Blue RPMs typically are placed six inches from the middle of the street on the side closest to the fire hydrant, the manual states. The placement is different, though, if the fire hydrant is near a freeway, intersection or turn lane.  

Red, white and yellow RPMs are mandatory nationwide. They are used as a positioning guide to enhance travel lanes at night or during poor weather conditions. 

Red RPMs signal drivers they are going in the wrong direction, while white and yellow ones are used contiguous with travel lanes — the broken or solid white and yellow lines in the street. 

RPMs can either be retroreflective or internally illuminated, according to the Federal Highway Administration's Manual on Uniform Traffic Control Devices. A retroreflective marker has a lens or sheet inside that mirrors a vehicle's headlights. Internally illuminated ones, much like the name suggests, burn steadily on their own. 

Installation and maintenance of blue RPMs falls on the local governmental agency that initially sought approval for them. Here's what Treasure Coast agencies do: 

St. Lucie County: The Utility Division contracts the job to Inframark, a national infrastructure services company based in Pennsylvania.

Indian River County: Sometimes the Utilities Department installs them, sometimes it hires a contractor, Director Vincent Burke said. 

Martin County: Fire Rescue recently took over the job from the Utilities Department, Fire Marshall Doug Killane said. When a new fire hydrant is installed, any crew member can pick up a marker from the department's inventory and install it. 

Editor's note: Catie Qs is an occasional feature produced by TCPalm Community Reporter Catie Wegman, who tries to find answers to your burning questions about anything and everything — the more bizarre the better. Contact her by email at catie.wegman@tcpalm.com, and follow her on Twitter and Instagram @Catie_Wegman and on Facebook @catiewegman1.