Signed at vs. signed in

Question:

Which is correct: signed at Ottawa or signed in Ottawa?

Answer:

Both signed at and signed in are correct. However, in legal documents such as contracts, conventions and agreements, the traditional expression signed at is more common. For example:

• International Convention Against the Taking of Hostages
  Signed at New York on 18 December 1979

The Gage Canadian Dictionary (2003) explains that both prepositions (in and at) indicate place or location. However, in emphasizes the idea of being inside or within boundaries, while at expresses exact position, such as a point on a map.