Try using NSUTF8StringEncoding
NSString *myUnencodedString = [NSString stringWithFormat:@"192.168.1.5/mobileapp?/signin=%@&%@",username,password]
NSString *encodedString = [myUnencodedString stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
NSURL *myURL = [[NSURL alloc] initWithString:encodedString]