How to attach a tag (digital signature) to a video ?

hi friends..
i want to insert a digital signature or a digital water mark.. (just to make things simple here for me i refer them as 'tag' or 'code')..

i am planning to make my own software for adding/inserting data and then decoding/retrieving the data from the code....

my questions ..
is it virtually possible for adding a code in the video file (i.e. in 3 to 4 frames placed equally in starting, between and ending of the clip .)

what type of tools i will require to do so ....

thanks you for reading .. :thumbsup:
awaiting replies :) :)