> My Telegram account can be synced on multiple PCs and devices, while Signal seems to be phone only.

I believe that is only temporary. The latest version of Signal hints at multi-device synchronization, though it appears to not be fully implemented. One example of this is the Chrome browser extension[0].

[0] https://github.com/WhisperSystems/Signal-Browser

Maybe for a synching feature it would be necessary to compromise on security of the data. The data is asymmetrically encrypted - so you'd have to synch it yourself by sending the data encrypted with you second phones key or you'd have to copy the private key itself. But I guess it would be possible. Though I don't miss this feature anyway.

Some settings in the latest Android beta of Signal indicate this is being worked on.