When should the first signs of rabies appear?

Variable. The virus has to travel to the brain so the further the bite is from the brain the longer it takes to manifest. So you die sooner from a bite to the face than one to the foot... http://www.cdc.gov/rabies/index.html.
Clinical rabies. The symptoms of rabies after a 'real' exposure usually average 3 weeks to 3 months for humans. Extremes can sometimes occur with the shortest incubation times of 4 days for bites to the eye or through the skull. The longest incubations are 'years' in duration - with 1, 5 and 10 or more years documented. Best to 'define' that exposure, then seek treatment before any symptoms develop. .
2 weeks to 3 months. The incubation period (time from getting the virus to getting first symptoms) is about 2 weeks to 3 months. When the symptoms first appear, it is too late already. Since rabies is fatal, rabies shots should start right away after exposure to the saliva (usually from a bite) of an infected animal.