CLEVELAND (AP) -- The city's transit system asked passengers to be extra vigilant for anything out of the ordinary on Thursday after a series of explosions rocked the London transit systems.
In addition to permanent signs that tell passengers to report potential danger, train and bus riders of Greater Cleveland Regional Transit Authority heard a recorded announcement Thursday instructing them to report unusual activity.
Spokesman Jerry Masek said there have been no threats, but Joseph Calabrese, the agency's chief executive and general manager, ordered a higher level of alertness among passengers and staff.
The Homeland Security Department asked authorities in major cities Thursday for heightened vigilance, but there were no immediate plans to raise the nation's threat level.
Cleveland Hopkins International Airport increased the number of patrols and bomb-sniffing dogs at points where the transit system's buses and trains drop of passengers, airport commissioner Fred Szabo said.
''We've been in constant communication with the Department of Homeland Security,'' Szabo said. ''They told us there is not a specific aviation threat at this point.''
Sharon Sears, spokeswoman for Dayton International Airport, said airport officials are waiting to hear from federal officials on whether to make security changes.
In the meantime, Sears said airport officials are telling employees to continue their practice of looking for suspicious behavior or unattended bags or packages.
Cherry Young, 27, of Dayton, a student at Sinclair Community College in downtown Dayton who rides city buses all the time, said the bombings scare her and she worries that it could happen in Dayton.
''There's not enough security on the buses,'' said Young, who plans to keep riding the buses despite her fear.
She said the city should either station uniformed security guards on the buses or consider searching passengers before they board.