How to distinguish mass concentration and density?
According to IUPAC's Green Book [1], both $γ$ and $ρ$ can be employed to denote mass concentration. Fragment of a table from the section 2.10 GENERAL CHEMISTRY [1, p. 48]:


  $$
\begin{array}{llll}
\hline
\text{Name} &amp; \text{Symbol} &amp; \text{Definition} &amp; \text{SI unit} \\
\hline
\ldots \\
\text{mass concentration, (mass density)} &amp; γ, ρ &amp; γ_\ce{B} = m_\ce{B}/V &amp; \pu{kg m-3} \\
\ldots \\
\hline
\end{array}
$$
  
  […]  In polymer science the word “concentration” and the symbol $c$ is normally used for mass concentration.


Also, from the SI Brochure, [2, p. 139]:


  $$
\begin{array}{lll}
\hline
\text{Derived quantity} &amp; \text{Typical symbol} &amp; \text{Derived unit expressed} \\
  &amp; \text{of quantity} &amp; \text{in terms of base units} \\
\hline
\ldots \\
\text{mass concentration} &amp; γ, ρ &amp; \pu{kg m-3} \\
\ldots \\
\hline
\end{array}
$$


References


IUPAC “Green Book” Quantities, Units, and Symbols in Physical Chemistry, 3rd ed.; Cohen, R. E., Mills, I., Eds.; IUPAC Recommendations; RSC Pub: Cambridge, UK, 2007. ISBN 978-0-85404-433-7.
BIPM. Le Système International d’unitès / The International System of Units (“The SI Brochure”), 9th ed.; Bureau international des poids et mesures: Sèvres, 2019.