Here are international Maritime flags from 21 to 29. Most of the flags in the twenties are tinged with an element of blue. But the nautical flag for 21 is reflective of 'Blackjack' - which is represented figuratively by an Ace of Spades and Queen of Hearts.
The Maritime flag for Twenty One
The Maritime Flag for Twenty-Two
This flag is loosely based upon the ICS flag for number two, but the colours are reversed and two extra dots are present.
The Maritime Flag for Twenty-Three
Originally France holds the ICS pattern for three, but for twenty-three Russia gets respects, or its Serbia? I guess it's whatever you want.
The Maritime Flag for Twenty-Four
Again this is based on the number fourteen, which is derivative of the ICS flag for four and NATO flag for four.
The Maritime Flag for Twenty-Five
Just as twenty-five has an un-noticed symmetry like 69, this flag is geometrically symmetrical.
The Maritime Flag for Twenty-Six
Can you see the six dots and two halves in the this flag that reflect two and six?
The Maritime Flag for Twenty-Seven
This is based upon NATO's flag for seven but with a Canadian accent, or rather Peruvian. Many nations get accidental representation in the official ICS flag chart which includes Japan, France, Denmark, England, Ukraine, Finland, Scotland, Costa Rica, Poland, Indonesia, Monaco, Honduras, Nicaragua, and El Salvador. It's only appropriate since Canada is the proverbial 'life-coast guard' of Earth. Canada like the Coast Guard is strong, intelligent, talented, peaceful, mostly friendly, official, and very very helpful.
The Maritime Flag for Twenty-Eight
This is based upon the ICS number two flag but is made up of eight parts: a yellow sun, three yellow stripes, three blue trapezoids, and large blue trapezoid holding the sun.
The Maritime Flag for Twenty-Nine
Since crosses appear so many times its only fair that some other spiritual symbols appear as well in this case a crescent moon and six pointed star.