select polygon by pressing u
material > lambert
right click diffuse icon
apply same image as base texture
click new ( ignore bump mapping parameter just leave them default )
select image clip
and do it for ambient icon in lambert property editor.
then you will find polygon operator stack in explore
and we need word texture to be overlapped on the base texture
I prepared the one with alpha image.
select the lambert and double click or click box in front of lambert
then you will see below property edior, (but actually diffuse icon and ambient icon turned into red cause it's arleady connected with base texture)
right click diffuse icon > blend with > image
and choose word texture and define the projection
do the same thing in ambient icon
finally select lambert parameter > press 7 to open render tree
you should find this structure of you can adjust like below
