Some Xs are red. Others were imbedded into what had been wet cement, then colored blue. All are only a few inches in size.
If "X marks the spot," San Antonio police may know why they were found scattered along residential street curbs in at least two subdivisions on the far North Side.
Sgt. Javier Salazar, SAPD spokesman, said the department's intelligence unit, north property crimes investigators and patrol officers were looking into the source of the mysterious markings.
"The prevailing theory now is that a company was selling their services door-to-door, then left Xs in front of the houses that weren't receptive," Salazar said.
If so, Salazar said it should give peace of mind to residents who may have worried the Xs were possibly used to alert burglars whether anyone was home.
He said leaving Xs on street curbs is not against the law, but SAPD is working to confirm which company is responsible.
Salazar said officers also will see if the blue Xs imbedded in concrete are connected to those left in red.
Salazar said at first it was thought the Xs possibly were used to indicate the location of utilities.
However, SAWS, CPS Energy, SA Public Works and Solid Waste Management report they do not use those type of markings.