The Capitol Corridor is an unreserved train with a certain amount of people who board without a ticket at the unstaffed stops. Conductors will often leave seat checks blank, instead orienting the seat check a certain way to indicate the stop. A vertical blank check on the side with no text may mean Sacramento while a vertical blank on the side with the text placed upside down may mean Davis, a horizontal blank with text to the left may mean Suisun/Fairfield, and so on and so forth.
Often times conductors will come through before the stop and collect the seat check and reuse it for someone else since nothing has been written on it. What this also means is the passenger can take the blank seat check before their stop and keep it. If the next conductor they see on another train uses letters (such as S for Sacramento, D for Davis, etc) on the seat check then the passenger can just pull out their check (of the appropriate color) and write the letter on with a sharpie. That check can then be reused any time they have a conductor that uses that method. I'd say the majority of the conductors do not write the station code on the check (for example O would be Oakland-Jack London instead of OKJ and OC would be Oakland Coliseum instead of OAC).
While this would generally would not work on LD trains, on non-reserved intercity (commuter like) trains with multiple stops and passengers boarding and alighting frequently there is a much higher potential for fraud. Also, conductors often times do not lift tickets after every stop as well so it is possible to get on and off the train without ever having a ticket lifted (thus riding for free and uncounted). I once rode from Emeryville to Davis without a conductor coming through the car to lift tickets at all (extreme, but true example). Usually they will come through at least every 2-3 stops at minimum to lift tickets.
It should also be noted that the printers are intended to also be used to print tickets purchased on board and receipts in the future to allow the sale of multi-ride tickets and the ability to validate tickets in the upcoming year. It is still in a testing phase.
While I hardly encourage any of those practices, working in transit the unfortunate truth is that fraud is more common than we would like or think. There are those out there who slice bar codes off transit tickets and place them on other ones to sell them to unsuspecting tourists on BART or who try to reprogram tickets to get unlimited rides. Printed seat checks are trying to keep people on their best behavior while also standardizing the format of each seat check used on the route.
