German Duden dictionary gives both anzeigen and (an)melden (bei der Polizei). 'Anzeigen' can also mean announce (an event) or advertise (a product) and 'eine Anzeige' is what you put in a newspaper or on a noticeboard to announce an event or to sell or buy a product or property.
Strange . . . I would have thought it would be an "ihn" vs. "ihm" difference, i.e. the basic structure would be "I will report/notify someone/something to somebody" so "I will report him" would be said with the direct object "ihn" and "I will notify him" ("I will report to him") would be said with the indirect object "ihm", but I see that it cannot be so simple, because "Sie" in you example is in the accusative too . . .
I'm sure you could use 'informieren' or 'benachrichtigen' for notify. 'Ich werde Sie (davon / darüber) informieren / benachrichtigen'. Also 'Bescheid wissen / sagen' is a useful way to say 'to know' or 'to tell'. Ich weiß Bescheid = I know; Können Sie mir Bescheid sagen = can you please inform / tell me?
I'm pretty sure 'eine Anzeige' can also mean an announcement or notice or advert that you put in a newspaper or on a notice board if you want to announce (an event, wedding etc) or advertise something you want to sell, or are looking to buy (eg a car or an apartment). So I thought this German sentence could perhaps also mean 'we will advertise / announce it' if the 'ihn' refers to a masculine noun eg einen Computer zum Verkauf or einen neuen Film im Kino?
Yes, that is one of the meanings of this verb (specifically regarding the police):
Dictionaries will keep you truer than digital translators will (which are notoriously bad with nuance). :)
When the sentence said "Ich werde ihn anzeigen" I got it wrong and it said the correct answer was " I will reveal you". When I answered this one as " We will reveal him" it said I was wrong as it is "We will report him". Am I wrong or does the meaning change depending on the subject/person?