these type of religious statues or other religious structures are all over Austria as well, funny enough I'v just installed about 15 of them on my layout. I don't know the origin of it but I assume they are a.) to remind you, your in catholic country or region, b.) may save guard your journey, c.) when go past acknowledge them. d.) they also come in brick or stone enclosures and differ in sizes.
I would think they've started in the Middle ages whereas suspicion and the devils work was prominent and it was a reminder when approaching such a sign you stop and do your religious bit and this should help you to continue your day without any trouble.
Religion played a much greater roll back than as today and it is apparent in most countries whereas in each town or village there was always a church and land around it was most probably owned by the church as well, it can be seen especially on escape to the country in England, each village sometimes has 2 or 3 churches from different religious nominators and such small communities are still very active today in church activities

John