Famed Swedish engraver Czeslaw Slania is renowned as a joke- ster.

So this summer, after U.S. Postal Service officials began a search for hidden marks on recent U.S. stamps, they said that a scrawl-like mark on a 1985 commemorative stamp, engraved by Slania, appeared to have been one of his pranks -- an upside-down signature included in violation of U.S. policy.

Yesterday, the Postal Service announced that the joke was on it.

The scrawl, one of three hidden marks said to be found on recent U.S. stamps, was actually part of the design for the stamp honoring World War I veterans, the Postal Service said.

Following the August announcement that an engraver at the Bureau of Engraving and Printing had added a tiny Star of David to a $1 stamp, postal spokesmen said they had discovered that Slania, the court engraver of Sweden, had added his signature to the veterans stamp.

Yesterday postal officials said an investigation that followed a complaint by Slania proved him correct. His engraving faithfully followed the artwork he was told to copy, officials said.

"Slania obviously did not add any unauthorized elements to the engraving," the announcement said.

A review showed that the lines believed to be Slania's signature were in the original stamp design, a recreation of a 1918 pastel drawing by Army combat artist Harvey Dunn, it said.

The bureau is reviewing dies used to print recent stamps following disclosure that engraver Kenneth Kipperman had added the Star of David to a 1986 stamp honoring Jewish immigrant Bernard Revel, founder of Yeshiva University. Results should be announced in several weeks, a bureau spokesman said.