There are three flags on these 1998 Italian stamps: Italy, Sardinia (also know as 'The four moors flag'), and the European Union.
The stamp celebrates the International Fair of Sardinia, held in Cagliari every year since 1948 in its current form. I don't know if Italian stamps valued in lira are still valid as postage (there was a 2 euro stamp on the card also).
And in the US flag stamps are ubiquitous. Here are two I received in the mail during the past two weeks.
On the left is 'U.S. Flag' designed from a photograph, issued in 2019, and on the right is a graphically designed 'U.S. Flag' issued in 2018. I hadn't noticed that they have the same name - in the past I remember the flag stamps having their own distinct names. The 2018 stamp takes its cue from another stamp issued in 2018 to commemorate the centenary of the Flag Act of 1818. The Flag Act formalized the design if the US flag - thirteen horizontal stripes and a star for each state - as well as the fact that changes to the flag after admission of a new state would always occur on Independence Day, July 4th.