The message read: "Report suspicious activity! Total Bull----! You have created a self fulfilling prophecy."
Numerous pieces of physical evidence were recovered from the scene of the package sent to the transportation department, State Fire Marshal William Barnard said, but police have not yet identified any suspects.
The packages, addressed to Gov. Martin O'Malley and to Transportation Secretary Beverley Swaim-Staley, have been taken to the FBI lab in Quantico, Va., for forensic analysis.
They were opened within a 15-minute period Thursday at state government buildings 20 miles apart.
The workers who opened the packages singed their fingers, but there were no significant injuries.
Soon after, mailrooms across Maryland were cleared and two other suspicious packages uncovered, though they turned out to be a toner cartridge and laptop batteries.
Explosive material wasn't found in either package that ignited and authorities aren't sure if any other dangerous packages are out there, but mailroom employees were back at work Friday. They had pictures of the packages and were advised to be vigilant about anything suspicious.
Meanwhile, the packages have prompted officials in at least four nearby states to be more vigilant.
O'Malley, a Democrat, had said previously that the mailing sent to him complained about highway signs that urge motorists to "Report Suspicious Activity" and give an 800 number.
"Somebody doesn't like seeing that sign," O'Malley said late Thursday.
A worker ripped the pull tab on the first package, addressed in typeface to the recently re-elected governor and adorned with holiday stamps, in Annapolis where mail for O'Malley's office is routinely checked. The building is just blocks from the governor's office, which is inside the State House in the heart of the capital.
An administrative assistant to Swaim-Staley opened the second package on the fourth floor of the Department of Transportation headquarters in Hanover, near the secretary's office.
Both had incendiary devices inside and produced puffs of smoke and a smell similar to a match being struck, authorities said.
Maryland's terrorism tip line is widely shown on overhead highway signs. The state also uses the signs to post information about missing children and, to the ire of some drivers, added real-time traffic estimates to major highways in March. Some commuters complained drivers slowed to read the signs and backed up traffic. At O'Malley's request, the state studied the issue and removed the real-time postings from one congested area on the Capital Beltway. There are 113 highway signs statewide.
U.S. Postal Inspector Frank Schissler, a spokesman for the Washington division of the inspection service, said Friday that investigators were examining postmarks and other exterior markings on the packages in an attempt to trace their origin.
The postal service also will examine its internal tracking data, Schissler said. Packages are tracked once they enter mail processing plants. But the packages did not have individual tracking numbers because they were sent by first-class mail, not registered mail or express mail, he said. Schissler also said that DNA analysis was likely.
A mail carrier was delivering and picking up mail Friday morning at the Jeffrey Building in Annapolis, where the first package was opened, and other state office buildings. Workers met the mail carrier's truck on the street near the governor's mansion to exchange outgoing mail for incoming mail. They declined to comment.
Rep. C.A. Dutch Ruppersberger, D-Md., said a return address on one of the packages turned out to be a Washington parking garage. Ruppersberger, a member of the House Intelligence Committee who was briefed on the mailings, said there were no apparent links to terrorist organizations.
"I believe this is what we call in intelligence a lone wolf situation, involving an individual who for whatever reason was upset with state government," Ruppersberger said.
The Department of Transportation is subjecting mail to additional scrutiny, but otherwise operations were back to normal Friday, spokesman Jack Cahalan said.
After the administrative assistant opened the package Thursday, she dropped it on the floor and someone pulled a fire alarm. Cahalan, who was on the fourth floor but did not see the package being opened, said he initially thought the alarm was a drill. About 250 people work in the four-story building, and the evacuation was orderly, he said.
"I've participated in more fire drills here than I ever did in elementary school," he said. "Everybody knows the drill; everybody knows what to do."
The FBI's joint terrorism task force was assisting in the investigation. A U.S. Homeland Security Department official said the department was aware of what happened and was monitoring.
Postal inspectors have identified 13 dangerous devices sent through the mail since 2005, and only one person was injured, according to the U.S. Postal Service. Inspectors made arrests in eight of those cases, said Schissler, who noted that the packages sent Thursday would not be classified as dangerous because they did not contain bombs.
In 2001, as the nation was still reeling from the 9/11 attacks, letters containing anthrax were sent to lawmakers and news organizations. Postal facilities, U.S. Capitol buildings and private offices were shut for inspection and cleaning. The anthrax spores killed five people and sickened 17.
Associated Press Writers Alex Dominguez and Kasey Jones in Baltimore, Sarah Brumfield and Jessica Gresko in Annapolis, Brian Witte and Norm Gomlak in Atlanta, and Eileen Sullivan and Alicia Caldwell in Washington contributed to this report.