Top and bottom horizontals are the 二 radical that 五 is filed under. They picture heaven above and earth below; the X in between is the cosmological interplay of yin and yang said in old commentaries to give rise to the five phases.
ideograph
五wǔ
five (inner crossed strokes)
The two crossing strokes between the heaven/earth lines are an abstract X-marker representing the interweaving of the five phases. They are not a standalone CJK glyph; treat them as the indicator that distinguishes 五 from a plain 二 and counts to five.
