Common Tern

Orange ring with a black two alpha-numeric code (letter/number).

note 1 : some rings have a bar separating letter and number.

Yellow ring with a black three alpha-numeric code (letter/number/number) (on one leg) and metal ring (on other leg).

note 1 : used codes are R01-R99 ; K01-K99,

note 2 : code to be read from bottom till top.

note 3 :

Dark-blue ring with a white three alpha-numeric code (on right leg) and metal ring (on left leg).

note 1 : birds ringed in The Netherlands.
note 2 : used codes are A00-A99 and 00A-99A.

White ring with a black three alpha code (starting letter 'K').

note 1 : project started in 2012, 50 birds ringed so far.

Black ring with a white 3 alpha-numeric code (on left leg) and metal ring (on right leg)

note 1 : birds ringed in the UK, county West Midlands.

note 2 : codes start with A01 - A99, C01 - C99, etc.

note 3 : 

Green ring with white 3 alpha-numeric code (starting letter 'I') (on left tarsus).

note 1 :

White ring with a black 3 alpha-numeric code (starting letter 'I') (on left tibia).

note 1 :

Blue ring with a white 3 alpha-numeric code (on right leg) and metal ring (on left leg).

note 1 : used codes are TAA-TZZ.
note 2 : all birds ringed in central Poland.

Combination of 2 c-rings and metal ring.

note 1 : for Manchester : yellow ring over metal ring (on right leg) and 1 c-ring (on left leg).  Year colour : 2006:blue , 2007:black ,  2008:red , 2009:white , 2010:orange , 2011:green.
note 2 : for Lancashire : white ring over metal ring (on right leg) and 1 c-ring (on left leg). Year colour : 2010:yellow , 2011:red.
 

White ring with black 3 alpha code (SAA -SZZ) (on right tarsus) and metal ring (on left tarsus). 

note 1 : exception codes with second letter (M, W, X) and third letter (M, W).

note 2 : this project starts running in Sečovlje Salina Nature Park (Slovenia) from april 2011.