A list of some commonly used guru initials:

ACBSP    A.C. Bhaktivedanta Swami Prabhupada
BBGS Bhakti Bhrnga Govinda Swami
BBS Bhakti Bhusana Swami
BCAIS Bhakti Caitanya Swami
BCS Bhakti Caru Swami
BGNS Bhakti Gauraya Narayana Swami
BJD Bhurijana Prabhu
BKG Bir Krsna Goswami
BRS Bhakti Raghava Swami
BSDS Bhakti Svarupa Damodara Swami
BTS Bhakti Tirtha Swami
BVMS Bhakti Vaidurya Madhava Swami
BVPS Bhaktividya Purna Swami
BVKS Bhakti Vikasa Swami
BVS Bhaktivaibhava Swami
CMS Candramauli Swami
DAS Devamrta Swami
DG Danavir Goswami
DDS Dhanurdhara Swami
GGS Gour Govinda Swami
GKG Gopal Krishna Goswami
GRS Giriraja Swami
GS Ganapati Swami
HDG Hridayananda Dasa Goswami
HKS Harikesa Swami
IDS Indradyumna Swami
IS Isvara Swami
JAS Jayadvaita Swami
JDG Jagadish das
JPS Jayapataka Swami
KCS Kavicandra Swami
KDS Krsna Das Swami
KKS Kadamba Kanana Swami
KRKS Krishna Kshetra Swami
LOK Lokanath Swami
MG Mukunda Goswami
MSD Madhusevita Prabhu
MVS Mahavishnu Swami
NRS Niranjana Swami
NYS Navayogendra Swami
PCD Purnacandra Prabhu
PD Paramananda Dasa Adhikari
PAS Prahladananda Swami
PDA Prithu Dasa Adhikari
PGS Param Gati Swami
PSDG Partha Sarathi Dasa Goswami
PTS Purusatraya Swami (Brazil)
PVS Prabhavisnu Swami
RGS Radha Govinda Swami
RNS Radhanatha Swami
RPS Romapada Swami
RSD Rohini Suta Prabhu
RTS Rtadhvaja Swami
RVSD Ravindra Svarupa Prabhu
SDA Sankarshan Das Adhikari
SDG Satsvarupa Dasa Goswami
SDHS Sridhar Swami
SKS Smita Krsna Swami (Sweden)
SNS Sacinandana Swami (Germany)
SOS Somaka Swami
SRS Sivarama Swami
SSM Subhag Swami
SS Suhotra Swami
TKG Tamal Krishna Goswami
TVS Trivikrama Swami
VS Varsana Swami
VVPS Vedavyasapriya Swami
VBD Virabahu Prabhu
VMS Vipramukhya Swami
   
One more acronym which is sometimes used:
SPY Srila Prabhupada's Youth