Ditto on what dunster said. If you belong to an HOA, there are usually Covenants, Conditions & Restrictions (CCR's). If you live in a subdivision, there may be restrictions set up by the developer. And villages may have rules about what you can have on the outside of your house if you live within the city limits.
Plus, if it's something that is visible from the street, it might impact the value of your neighbor's house (either positively or negatively, depending on the area) so if you don't want to start a neighborhood feud, you might mention it to the neighbor & see what they think of it. If it's something that can be easily taken down, it's probably not a big deal. If you plan to make it a permanent attachment to your house, in certain areas that could cause problems. In rural areas, the homes are far enough apart that what you paint/affix on the side of your house/barn is not even visible from the nearest neighbor's property.