Another encrypted messaging app Telegram was at the third spot in downloads and number two in MAUs, according to data provided by app analytics firm App Annie.
The signal is gaining immense popularity owing to its simplicity and focus on privacy.
People are switching to Signal in record numbers because companies who sell ads have a harder time focusing on the things that users actually want.
According to App Annie, the top apps by downloads, consumer spend and MAU across Apple App Store and Google Play were TikTok, YouTube and Facebook in the January-March quarter.
Homegrown app MX Takatak, a local alternative to TikTok, was also seen as the fastest growing app by downloads in the quarter.
TikTok led the top downloads chart, followed by Facebook and Instagram.