If you want to try this yourself, I suggest using fine markers. Unfortunately I only had regular Sharpies to hand.
So yes, they're no where near as good as the ones you see on Pinterest haha. I'm going to get myself some fine markers I think and write inspirational quotes on others at a later date and put them back on Southsea seafront. These are quite fun to do and I'm sure kids would love having a go =)