Solar is not great for signage. There are solar suppliers you can buy the necessary parts from. Batteries are just deep cycle marine batteries, solar guys will sell those too. If it gets cold where installing, the battery enclosure will need to be heated. Use as low power of an LED as you can and limit LED usage through your design, push through is a good out for that. Pre-calculate your wattage and give yourself at least twice the output to reduce strain on the batteries.
In my experience, the larger of a solar setup you need, the more cost prohibitive it becomes. Unless this is going literally in the middle of nowhere, trenching power tends to be cheaper. Solar has maintenance costs people tend to ignore until they need to spend another 2k on batteries a few years down the line.