Assuming you make many plaques the same size and shape I would make a pattern and route the shape on the ends. Of course you would have to rough cut it with a bandsaw first but if you route the ends it will be finished enough where you wouldn't have to sand it. It wouldn't have quite the same square inside corners as the one shown but I don't think most folks would object to a small radius there.
Cutting rounded edges for wood plaque
What would be the best way to cut rounded edges as pictured. I make signs using this style sign. To used to buy the sign pre made for $8 but quickly realized how much it ate into the profit. I've been making them at home with a scroll saw then routing the edges. It takes forever and has lots of room for error due to the edge being cut free hand. Sometimes I have 30 orders a month for the sign and I need to figure out a quicker way to make them. Any advise/tips would be greatly appreciated!
