The following features in Microsoft Dynamics GP are not supported in Signature:

RM Receivable Voiding process is not compatible with posted Signature invoices (created in Service Management, Job Cost, or Equipment Management).
Scheduled Payments functionality in Receivables.
Batch Service Invoicing does not support payment terms.
Lockbox
When using the Payables Transaction Entry Distribution window, for Service Management or Job Cost transactions, you cannot use a Distribution Type of CASH, PAY, or UNIT.
Multi-bin Inventory
Customer Combiner and Modifier
Vendor Combiner and Modifier
Pay Code Start and End Dates
The Professional Services Tools Library that is included with Microsoft Dynamics GP modifies or combines data within GP. The data is not changed within Signature. Using the Professional Services Tools Library, you could modify, change, or delete things that can never be fixed. There is no UNDO button.
We do not test our Signature solutions for compatibility with Microsoft Dynamics GP Project, Field Service, or HR Payroll.
Using Letter Writer Assistant to merge data from Microsoft Dynamics GP to Microsoft Word's Mail Merge
Copying of purchase orders using Copy PO function
Purchase order returns with serialized inventory items
Date Effective Tax Rates
Allowing summary-level tax edits
Specifying tax details for automatic tax calculations in Company Setup is not supported.
Calculating tax rebates
Calculating taxes in General Ledger
Merging trade discounts and markdown distributions in Sales
Merging trade discounts and markdown distributions in Purchasing
Calculating terms discount before taxes
Promotional and free items
Service transactions using accounts set
Transaction batches with a frequency other than single-use
Payables recurring batch / entering cash receipts assigned to a job in a recurring batch
Pay Code Modifier
Automatic Overtime payroll option
PO Tolerance - shortages
Intercompany fixed asset transfers
Editing Payroll history records
Purchase order receivings with shipments followed by invoice match when the tax is included with the item price.
Microsoft added a cost warning that was added in Microsoft Dynamics GP 2010 and 2013 for cost variances. If you invoice a single shipment using more than one invoice and the costs of those invoices differ, you will get a warning that your costs don't match. Posting updates the total quantity of the purchase receipt with this cost and your inventory and general ledger will not balance. You can proceed with the transaction, save it to a batch, or delete it. Only this warning is new, this is not a change to functionality. For more information about this warning, see the Dynamics GP Support and Services Blog.
Assigning suggested sales item to an item
Analyzing suggested sales items
Using document attachments in Payables Management transactions such as payables invoice, payables finance charge, payables miscellaneous charge, and payables credit memo.
Purchase requisitions
Payroll Timecard workflow (introduced in Microsoft Dynamics GP 2013 R2)
The Self-Service role, in the Select GP Home Page window off the Customize Home Page window, is not compatible with accessing TimeTrack's Time Card Entry window.
Procurement and Time Management content areas in the Customize Home page window.
Using the Report Assignments window to assign Signature SRS reports to print from specific transaction windows.
When copying journal entries from Excel and pasting into the General Ledger transaction entry window, the account entries, debits, and credits come through, but you will need to enter the Signature information manually.
Workflow for SharePoint
The Warn if vendor has existing purchase order option is not compatible with the Contract Agreement window in Job Cost.
Project Level Invoicing does not support multi-currency or payment terms with discounts.

Additional Products

In general, Signature products may not be compatible with Microsoft Dynamics GP's additional products. The following products do not support Signature transactions:

Sales Order module - SOP returns from invoice documents in Service Advantage
PO Generator

Browser not supported