Try
HSERIN [WAIT("CSQ: "),DEC Signal]
SEROUT2 ....[DEC Signal]
You don't have 13 chars, after AT+CSQ:...
From manual
STR ArrayVar\n{\c} Receive string of n characters optionally ended in character c
So If you want to string end after receiving CRLF
Try this
Serialdata var byte[4]
HSERIN 4000, GSM_CHECK, [WAIT("AT+CSQ"),STR Serialdata\4\13]