It sounds like your boss is more skilled at writing his own name than writing the actual reports that bear it. However, before barging into his office and demanding that this outrageous breach be undone, there are some other elements to consider.
For example, there can be departmental projects that, from the outset, are delegated to the staff with the clear stipulation that they will go to the intended recipient under the department manager's signature. Some departments may even have a standard operating procedure wherein reports come from the department itself rather than from specific individuals within it. In addition, there are situations where managers take the reports prepared by their staff, make some key revisions, and submit them under their own name
At the very least, all of this must be clarified with the employees at the outset. Anything short of that is deceitful, unethical, and unacceptable. If your boss has simply usurped your work and passed it off as his own, that is wrong. And, it would be wrong of you to say nothing about it.
You should meet with your manager, go over the situation, listen carefully to what he has to say, and then determine your next step. If he has overstepped his bounds, you may need to overstep him to resolve the matter.
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