Hashem tells Moshe, "Si'u Kol Rosh Kol Adas Bnei Yisroel; Take a census of Bnei Yisrael." After the count, Moshe comes up with number 603,550. Rav Moshe Singer says there is a Remez to the total population right in the words of Hashem's command.
Bnei Yisrael is gematria 603. Rosh Kol without the Aleph is 550 or 603,550. The Aleph? That is for Anochi, the Echad Yachid U'Miyuchad, Hashem, who promised to come out of Mitzrayim together with Am Yisrael.