RECTIFICATION
When the subject has no idea when he was born.

It is possible to work out a rising sign by a process of elimination. This is not easy and it requires a thorough ¬knowledge of energies and characteristics of each rising sign.
If the subject does not resemble his Sun sign, then try to work out what sign he does resemble   the chances are that he will be projecting his rising sign.

The second step is to ask a few questions about the CHILDHOOD AND BACKGROUND. The following suggestions may prove helpful.

1 If the subject was the eldest child or the most responsible one in the family, he may have been Cancer, Leo, Capricorn, Scorpio or even Aquarius on the Ascendant.

2 If he was the youngest or the least likely to take the lead, this would point towards Gemini, Virgo, Sagittarius or Pisces.

3 If he was loved just because he existed, without having to prove himself to his parents, then his rising sign could be Cancer, Leo, Libra, Sagittarius, Capricorn or Aquarius.

4 If he was only approved of, or even loved, because he behaved in an acceptable, or passed exams to order, then he could have Virgo, or Pisces rising.

5 If he really didn't fit in anywhere as a child he may have had Aries, Gemini or Scorpio rising.

6 Closeness to the mother (or other nurturing figures), would be shown by Taurus, Cancer, Libra and Capricorn; while closeness to the father would indicate Taurus, Leo, Capricorn and Aquarius.

7 A love/hate relationship with one (or both) of the parents might point to Scorpio or Pisces. Parents who were not interested in the child and fobbed him off with things rather than love suggest Taurus, Leo, Libra possibly Scorpio or Sagittarius.

8 A cautious shy approach during childhood would be shown by a feminine/negative sign on the ascendant, while an extroverted child or one who was expected to act in an extrovert or even  rather macho manner, would be Aries, Gemini, Leo or Sagittarius.

9 If by this process of elimination, you come up with two possible signs, make up two charts with the Ascendant placed in the middle decanate of each of the two signs.


FINE TUNING –

Ask the subject what  happened using SOLAR ARC DEGREE METHOD, works exceptionally well for triggering events in childhood (and indeed adult life).

Also if your subject has planets in the twelfth house, progress each planet 1' degree until it conjuncts the Ascendant. What happened at that age? Same applies to planets in the first house, progress the ¬Ascendant down 1' degree until in conjuncts a planet. What happened at that age?