Leg Ringing

There are a lot of people who carry out bird ringing on reserves & other places for various reasons. Normally there should be a code of letters or numbers on the yellow ring, the silver ring is only useful if the bird dies or is recaptured as it also gives details of the "ringer". Have a look on this page, there are several ones with yellow on the left leg cr-birding.org/colourprojects;tid_2=&tid=All&tid_1=All&tid_4=All&tid_5=All  

I hope this helps. If you can take a photo the code might be readable.