  The baryon form factor of charged pions arises since isospin symmetry is
broken with unequal up and down quark masses, $m_d>m_u$, as well as
electromagnetic effects. We obtain estimates for this basic property in two
phenomenological ways: from simple constituent quark models, as well as from
fitting the $e^+e^- \to \pi^+ \pi^-$ data. All our methods yield the result
that the baryon mean square radius, extracted from the slope of the form
factor, is positive for $\pi^+$, hence a picture where the outer region has a
net baryon, and the inner region a net antibaryon density, both compensating
each other such that the total baryon number is zero. For $\pi^-$ the effect is
equal and opposite. We estimate the corresponding mean squared baryon radius as
$\langle r^2 \rangle_B^{\pi^{+}} = (0.03-0.04~{\rm fm})^2$.
