WINMILL MARK CAMPBELL purchased ~$402K in Global Self Storage, Inc. stock
Global Self Storage, Inc. (SELF) · Data via SEC EDGAR Form 4
Price Performance · 10 days before → 90 days after trade
▲ = insider buy date
90-day return
+4.3%
Trade Details · Public SEC Filing
Insider
WINMILL MARK CAMPBELL
Role
—
Transaction
Open-Market Purchase
Approx. Value
~$402K
Trade Date
Dec 5, 2025
Company
Global Self Storage, Inc.
Ticker
SELFSource
SEC EDGAR Form 4
Why This Trade Stands Out
Strong conviction signal
Scored above average across multiple factors. Roughly 15% of insider trades qualify as Strong.
~$402K purchase
A meaningful investment of personal capital. The average insider purchase is around $150K, putting this in the typical range for serious positions.
3 insiders traded in the same window
When multiple insiders independently buy within 30 days, it's called a cluster. Studies show clustered insider purchases outperform solo trades significantly, because several people with inside knowledge are reaching the same conclusion.
+4.3% in 90 days
Measured from trade date to 90 days later. We track the performance of every insider trade to identify which insiders consistently make profitable moves.
How good is WINMILL MARK CAMPBELL at picking stocks?
Full track record: win rate, average return, and performance vs S&P 500
WINMILL MARK CAMPBELL wasn't the only one buying.
3 insiders at Global Self Storage, Inc. traded within the same 30-day window.
See who else bought · FreeOn December 5, 2025, WINMILL MARK CAMPBELL — a corporate insider at Global Self Storage, Inc. — filed a Form 4 with the SEC disclosing an open-market purchase of approximately ~$402K in Global Self Storage, Inc. (SELF) stock.
This transaction was part of a cluster — 3 insiders at Global Self Storage, Inc. made open-market purchases within the same 30-day window. Cluster activity from multiple independent insiders is one of the most studied patterns in insider trading research.
Under Section 16(a) of the Securities Exchange Act of 1934, corporate insiders must report all open-market stock transactions to the SEC within two business days. These filings — known as Form 4s — are publicly available on the SEC's EDGAR database. VeritySignals filters and scores the full Form 4 stream to surface high-conviction signals like this one.
In the 90 days following this trade, SELF returned +4.3%
VeritySignals Conviction Analysis
Full Conviction Analysis
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All data sourced from publicly available SEC Form 4 filings via EDGAR · Not financial advice · Past performance does not guarantee future results.
At a Glance
More SELF Insider Activity
WINMILL MARK CAMPBELL
May 14, 2026
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WINMILL MARK CAMPBELL
May 14, 2026
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WINMILL MARK CAMPBELL
Dec 1, 2025
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STRONG
WINMILL & CO. INC
Nov 28, 2025
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How to Read Insider Trades
What is this?
When company executives buy or sell their own stock, they must report it to the SEC within 2 days. These public filings reveal what the people who know the company best are doing with their own money.
Why does it matter?
Insiders can sell for many reasons (taxes, diversification, expenses), but they generally only buy for one: they think the stock is going up. That's why insider purchases are more predictive than sales.
What makes a trade "strong"?
We score trades on 15+ factors: the insider's role (CEO > director), trade size relative to their salary, whether other insiders also bought (clusters), and historical accuracy of the insider.
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