However good you are at telling the truth, avoid signing into a reception register with the reason as personal. Some organizations do not give you a chance to proceed to see the one you wanted to see with the argument that personal matters are no office business. I advise you for once to stick to the purpose of your visit being official.
It is also very important to always have the telephone number of the one you want to see. There are times when queues are really long or the process very bureaucratic, it helps ringing the one you want to see. In some instances he can even collect you from the reception.