"The writing is on the wall?" joke

One morning, President Reagan woke up to a beautiful snowy noon. He
looked out of his window upon the snow-covered White House lawn and
marveled at its beauty. Then he noticed something. Yellow lines in
the snow. On further investigation, our President realized that the
lines spelled out "Reagan Sucks" in urine. Furious, he called the
Washington, DC police and demanded to know who had inscribed these
blasphemous words on his lawn. After a lengthy investigation, the
police found no clues.
Later that afternoon, after a brief snowfall, the president awoke
again to find the same words once more decorating the new-fallen
snow. This time, President Ron called the FBI and ordered them to
find out who was responsible. The FBI too mounted a massive
investigation, but were only able to determine that no intruder had
access to the White House lawn and therefore the perpetrator had to
be someone on his own staff.
When the next day, the same insults were discovered on a new blanket
of snow, Old Ron decided to leave no stone unturned. He asked the
entire US military to get to the bottom of this conspiracy. By
dinnertime, the Secretary of Defense had some bad news for Mr.
Reagan.
"I'm afraid," he said, "that the urine sample come from none other
than the Secretary of State, George Schultz."
"This is terrible," said the president.
"I'm afraid I have more bad news," said the secretary.
"What could be worse," said Reagan, "than finding out that George,
the only member of my administration not to be involved in a
scandal, is involved in this conspiracy?"
"Well, you see Mr. President, it was written in Nancy's handwriting."