The posters irritate me, too, despite being very pro-feeding. Putting up posters is an easily measurable thing to do in order to tick a box saying that breastfeeding is being encouraged, when in reality a poster is zero support to a woman with soreness and a screaming baby in the wee small hours of the morning.
Poster with phone number of breastfeeding counsellor, or suggesting latching positions, or strategies for dealing with sleep deprivation - all great. I would really like to see posters in maternity wards explaining the early stages - what colostrum does, what happens when milk comes in, etc.
I am not fond of the saintly breastfeeder poster, nor the guilt trippy ones, because they leave women with a sense that they can't possibly measure up. In the fraught early days, it's a very short step to "This isn't like poster at all, I must not be cut out for this, I give up."
When my first was a fortnight old, I saw a cartoon depicting a breastfeeding mum sitting in a very messy room. The baby was wailing loudly with tears rolling down her face, and so was the mum. It was so funny and so true. I found that so much more encouraging than the posters that invited me to compare myself with ubermums.