This is because in the book, the symbol is most likely compared to being a 'triangular eye'
An odd symbol, rather like a triangular eye, glistened from a golden chain around his neck - p117, Ch8: The Wedding
Above what Harry assumed was the title of the story (being unable to read runes, he could not be sure), there was a picture of what looked like a triangular eye, its pupil crossed by a vertical line - p259, Ch16: Godric's Hollow
'The Elder Wand,' he said, and he drew a straight vertical line upon the parchment. 'The Resurrection Stone,' he said and he added a circle on top of the line. 'The Cloak of Invisibility,' he finished, enclosing both line and circle in a triangle to make the symbol that so intrigued Hermione. 'Together,' he said,'the Deathly Hallows.' - p332, Ch21: The Tale of the Three Brothers
It struck me that the second symbol is much more likely to be mistaken for a triangular eye than the first. In addition, the way Xenophilius Lovegood drew the symbol also implies that the Wand's line was not meant to extend past the circle of the Stone. The circle was added on top of the line, not on the bottom half of the line. Admittedly, this is open to interpretation.
As a follow-up question: Has the symbol for the Hallows always been the first symbol, or was it changed when the movies came out?