Help identifying badge

[Rm567]

Hello, I'd appreciate some help identifying this badge.

I belive its to the royal engineers, who were attached to the 57th division?

However I'm unsure what 'sl' means. Can anyone shed some light on this?

Thanks!

[Sonofacqms]

Showing the reverse of any badge is always a help in identifying what it is, this looks like a gilt collar badge or an officers F/S cap badge, but could be a sweetheart brooch.

Rob

[badgecollector]

without seeing the back it looks like a sweethearts badge.
could sl be for searchlight?
i know its normally RA but where they also RE at some point?
bc

[mike_vee]

Could the 'sl' stand for "second line" ?

On 31 August 1914 the War Office authorised the formation of a reserve or 2nd-Line unit for each Territorial Force (TF) unit that was proceeding on overseas service. The 2nd West Lancashire Division came into existence in November 1914, composed of 2nd-Line duplicates of the battalions of the peacetime West Lancashire Division that were due to be sent overseas. The 1st-Line division was temporarily dispersed as its units went to France piecemeal, many of the divisional staff and support elements transferring to the new formation, which became 57th (2nd West Lancashire) Division in August 1915.

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[Rm567]

It's a sweetheart badge and it's engraved to the rear with Jan 31st 1917

[Phil2M]

Looks like BL to me?