even if they are sometimes written on with felt tip pen.
I recall someone making a thread about 'people scribbling on planes' in this forum.... the reasons given were as you stated... for ease of cabin crew filling out paperwork etc...
Also, it's sometimes handy to see if the airline you are flying on has a naming'rego "family"... e.g. Virgin Blue aircraft all (except for one in the past I believe, the red-nosed one) start with 'V'... most 737-700s are
VB- while -800's are VO- or VU- (however there are some exceptions) it should also be possible to find the N number or rego if your aircraft has a name below the cockpit windows...
(I too like to know which a/c I am flying on, as well... just a little habit of mine...
)