The national flag of the Principality of Monaco is identical to the flag of Indonesia. The combination of red-white can be also found in the flag of Poland and Singapore.
The flag of Monaco has two equal horizontal bands, one red (top) and the other one white (bottom), both of which have been the heraldic colours of the House of Grimaldi since at least 1339.
Monaco’s original flag, which was similar to its current Princely flag with an older version of its coat of arms, was in use from the Principality’s early days (except during its annexation to France from 1793 to 1814) until the present. A simpler bicolour design was adopted on 4 April 1881, under Charles III.
Interestingly, the flag of Indonesia is graphically identical to the Monaco one, with differences in their dimension ratios (Monaco’s at 4:5 and Indonesia’s at 2:3), and the shade of red is darker on the flag of Monaco. The Indonesian flag was adopted in 1945.
The flag of Poland, originally adopted in 1807, is also very similar to that of Monaco, but with the colours reversed - white on top and red on the bottom.
The flag of Singapore, adopted in 1959, also uses the similar red-white design, adding in the upper left corner, a white crescent moon and five white stars forming a circle around it. In their flag, the red symbolises universal brotherhood and equality of man; white stands for pervading and everlasting purity and virtue.
Monaco’s princely flag (or government flag) 
Personal standard of H.S.H. Prince Albert II
One can see in Monaco both the Princely flag and the personal standard of Albert II.
Monaco’s Princely flag (or government flag) consists of the full achievement of the coat of arms on a white background. It is flown at the Prince’s palace, government offices, in the presence of government officials, and as an ensign on the Prince’s yacht.
The personal standard of Prince Albert II consists of the Crown of Monaco over two opposing “A” letters, on a white background. It is only used in his immediate presence, particularly on cars in which he travels. It is often seen with a gold fringe on the top, bottom and right, which is one-ninth the height of the white field.
